# Simple DIY Drop Checker (V2 is Alive! 3/31)



## NatCh (Feb 23, 2011)

Very interesting. Now my own noggin cogs are crankin'. Thank you!


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## Loop (Jan 8, 2011)

No problem. Just trying to throw out an idea I had incase anyone was interested. I wanted to find something that was cheap, easy, and reasonably atractive. I think I'm going to look for a container with more than a 1/2" opening so it would have more surface area for a quicker reading, but it might be hard to find that on such a small container. I thought about just using something with a funnel shape on the end, but I think it would be getting too bulky at that point. It's already about 3" tall so I didn't want to make it any bigger.


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## scapegoat (Jun 3, 2010)

i saw those items at the dollar store when i went searching for a DIY drop checker... i looked at it and looked at it... and wondered how i was going to use it.

now i know... i over thought it, this is so simple


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## Loop (Jan 8, 2011)

scapegoat said:


> i saw those items at the dollar store when i went searching for a DIY drop checker... i looked at it and looked at it... and wondered how i was going to use it.
> 
> now i know... i over thought it, this is so simple


I knew being simple-minded was going to payoff some day :confused1:


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## Loop (Jan 8, 2011)

OK, so boredom hit me again this evening, and I was staring at my drop checker thinking what can I do to make this work better. So I would like to present to you

*Simple Drop Checker V2*

I didn't like having such a small surface area to the water with a 3/8"ID tube because I was sure that the response time was going to be pretty slow to changes in CO2. I was still daydreaming about the things I want to try when I get some acrylic tubing, and I remembered the methods used here for making the DIY acrylic lily pipes and wondered if it would work on vinyl tubing as well. Well it does.










I took some of my leftover tubing that I had, and gave it a try. I took a piece about 6" long, and capped off one end of it. I heated the tubing in about a 3" long section with a heat gun on low. Keeping it moving so I didn't burn, blister, or discolor the tubing. Heated it until it felt a little soft and sticky, and blew into the open end of the tube. At first I had to blow a little hard to get it to start stretching, but once it did it stretched faster. On the first try, it started slow and then got big and popped a hole in the tubing. The second try I just let it stretch a little, heated and blew again slowly about 3-4 times until it got to a decent size, and I didn't think it would safely go much larger. Then I cut the tubing in the middle of the blown area, and cut the other end of the tube to the length that I needed. Then just install in the glass container again like before. 

This is a little more work, but it's not too bad and it solves two problems. Now you can't push the tube in too far to get it back out later for changing your solution. Also the surface area is much larger for faster readings. The original tubes inside diameter was only 3/8". Now the diameter is 13/16". If my math is right that means that the total surface area has increased to about 369% over the original design:icon_eek: (<-someone smart check that math). Hopefully it is a little faster now. I'll test as soon as I get some more solution to see how long it takes to change.

Here is a size comparison of the standard tubing vs blown tubing











Whatcha think?


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## Loop (Jan 8, 2011)

Bueller.......Bueller.......Bueller

No Comments? 
"Terrible idea" 
"Good job"
"Loop's a moron" 
"Might work better if _____"

I'm willing to accept any of those


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## Betta Maniac (Dec 3, 2010)

Very cool!


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## farmhand (Jun 25, 2009)

Loop said:


> "Loop's a moron"


We don't know yet???


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## tuffgong (Apr 13, 2010)

Nice work! DIY drives this hobby for me!


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## redfishsc (Aug 29, 2010)

Again, this is shamefully simple and awesome! Nice work!


This theoretically could be reproduced using acrylic instead of tubing (you'd need a dab of silicone to permanently seal it) if you have the right shape to heat-form it,. 


I've seen people make bowls out of acrylic scraps by putting a ceramic bowl in the oven, with the acrylic sheet laying on top of it, and as the oven gently heats the acrylic, gravity causes it to droop and conform to the bowl. Removing it and letting it cool leaves you with something that's fairly smooth and nearly flawless in shape. 


A metal funnel would probably work well for this but it would have to be a tiny one, and I don't know where you'd find such an animal.


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## Loop (Jan 8, 2011)

redfishsc said:


> This theoretically could be reproduced using acrylic instead of tubing (you'd need a dab of silicone to permanently seal it)


But if you glue it in, you can't pull it back out to change the solution out.


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## redfishsc (Aug 29, 2010)

Flip the bottle right-side up, pour the fluid in through the tube or acrylic. 

Tile the bottle sideways carefully, until it's upside down. Some may dribble out, but you don't need a large amount of the indicator solution. 

The amount of solution you end up with will be a function of how much fluid it will hold sitting sideways (ie, halfway to the "upside down" position). With the way you have it designed, it looks to me like this would still be plenty of indicator fluid.


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## Loop (Jan 8, 2011)

I know you can fill it that way, because that's what I have been doing with this one. I can't see how you could get the fluid back out though. From what I've read you should change it every now and then, and I couldn't think of a way to do that if the tube was permanently in there. Is there some simple thing I'm overlooking here or just a confusion on what one of us was saying?:icon_conf


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## redfishsc (Aug 29, 2010)

Yeah, I can see getting it back out being a pain in the butt lol. I misread your statement, sorry 

You could flush it out with water at the sink, and siphon the remaining stuff out using airline tubing. I have a small pile of oral syringes around the house that I once used to feed coral in my reef, so slurping out 30-50cc of fluid is a piece of cake .


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## Loop (Jan 8, 2011)

True, I didn't think of using a small syringe.


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## orchidman (Dec 15, 2010)

why would it need to be glued? if there isnt a need for glue, i think glue would definitely make it harder


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## Loop (Jan 8, 2011)

orchidman said:


> why would it need to be glued? if there isnt a need for glue, i think glue would definitely make it harder


He's saying if you used an acrylic tube you would have to glue it to prevent leaks. With the vinyl tubing I used it's not an issue as long as it fits in the opening tight.


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## Loop (Jan 8, 2011)

redfishsc said:


> A metal funnel would probably work well for this but it would have to be a tiny one, and I don't know where you'd find such an animal.


 
This comment got me to think again about the funnel idea. I googled "glass funnel" because I thought it wouldn't look too bad if there were any small ones. I found these on Amazon  that you could probably use for the bottom if they make some small ones. Not sure what the outside diameter is of the skinny part of the funnel though. Might be a problem if it's too fat to fit the tubing, but would give you a nice large size opening on the bottom. I'm sure there are some pretty creative drop checker desings that could be made using these funnels as a starting point also. I've already had a few ideas while typing this.


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## Loop (Jan 8, 2011)

I've got good news and bad news. 

The good news is, it works.  

The bad news is, I'm not sure how long it took to respond. 

I put it in the tank around 4:15 - 4:30. Then shortly after I got a call about some work related stuff. Had to check some emails and make some calls for work and I forgot to check on it. 

At around 6:30 I thought "OH $#!%, the drop checker!". Went to look at it and it was green. So I know it works in atleast 2 hours:icon_roll

How long do the standard little ADA/Chinese knockoffs take? I've never had one before.



Here's a pic of it in action. Brace yourself for all the action!


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## redfishsc (Aug 29, 2010)

Well, a 2 hour reaction time is a LOT better than my 3-week waiting time since I only check the pH against the alkalinity for CO2 levels when doing it the old school way


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## Loop (Jan 8, 2011)

redfishsc said:


> Well, a 2 hour reaction time is a LOT better than my 3-week waiting time since I only check the pH against the alkalinity for CO2 levels when doing it the old school way


lol  Yeah I guess I can't complain too much considering that. Plus the fact that it's under $2 and only takes about 15 minutes to make with the blown tube.


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## orchidman (Dec 15, 2010)

thats pretty sick! imma have to try that


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## Loop (Jan 8, 2011)

orchidman said:


> thats pretty sick! imma have to try that


Go for it. It couldn't be much simpler than this. 

I would suggest to anyone that is making one with the blown tubing at the bottom to buy a little extra. I originally bought 2ft of it just because it was so cheap, and it came in handy to have the extra when I messed up the first try. Your probably going to need at least 6 inches for each attempt because the tubing gets a little too hot in the heated section to hold comfortably. Good luck, and post pics here if anybody tries it or does something differently. I'm sure there are ways to keep this really simple and improve it or use other materials. roud:


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## larams67 (Jan 24, 2006)

How big does the bottle need to be? I have some tiny glass ones that hold around 5ml liquid with a .25 opening. Do you think that is to small?


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## smannell (Jan 10, 2009)

What are you using for your test solution/reagent (ie the green liquid)? Can you make your own using the chemicals from kH & pH test kits? I live in the middle of nowhere, so anything that normally comes from a local pet store requires an internet purchase or a 90 minute drive.


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## Loop (Jan 8, 2011)

larams67 said:


> How big does the bottle need to be? I have some tiny glass ones that hold around 5ml liquid with a .25 opening. Do you think that is to small?


That might be a little small to work with, but I'm not sure. I'm just not sure if you will have enough room in the opening for a tube. I think a good minimum size to look for would be a 1/2" opening, maybe 3/8" but that's still pretty small. Maybe something that holds at least 15-20 ml because the tube will take up a lot of the space inside. The package that mine came in says "1 FL OZ (30 ml)" and it is a little bigger than it needs to be. 





smannell said:


> What are you using for your test solution/reagent (ie the green liquid)? Can you make your own using the chemicals from kH & pH test kits? I live in the middle of nowhere, so anything that normally comes from a local pet store requires an internet purchase or a 90 minute drive.


I used some 4dKH solution and a couple drops of ph indicator (bromothymol blue) from my API test kit. I ordered the 4dKH online, but you can make it yourself. There are write-ups online for ways to make it, but I just didn't feel like going through the trouble when it's like $5 to order some and get it in 2 or 3 days. I think someone here was selling some in the Swap & Shop recently, and it's usually available on E b a y.


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## smannell (Jan 10, 2009)

Thanks for the info. Once I have the 4dKH solution, is the amount of pH indicator critical? My pH test kit calls for three drops of test solution for 5mL of water.

Also, I found a good source for small glass containers: empty salt & pepper shakers. They even have a nice look to them. The ones I found had an opening of .700", so with a little muscle and possibly some hot water to soften the tubing; a piece of 3/4" OD clear vinyl/acrylic/pvc tubing wedges into the opening quite nicely. Any grocery store or discount outlet should have a variety of sizes & shapes for a few bucks.


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## Loop (Jan 8, 2011)

The amount of ph indicator isn't any specific amount. Just a few drops until the coloring is dark enough that you can easily see it. I think I put around 4 in mine, but I wasn't really paying much attention. Just until I could see it well.


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## Hoppy (Dec 24, 2005)

Loop said:


> This comment got me to think again about the funnel idea. I googled "glass funnel" because I thought it wouldn't look too bad if there were any small ones. I found these on Amazon  that you could probably use for the bottom if they make some small ones. Not sure what the outside diameter is of the skinny part of the funnel though. Might be a problem if it's too fat to fit the tubing, but would give you a nice large size opening on the bottom. I'm sure there are some pretty creative drop checker desings that could be made using these funnels as a starting point also. I've already had a few ideas while typing this.


Here is one way, involving a little work, to make a good DC from that funnel:























Cut off the stem on the funnel, cut off the top of a small glass bottle, and silicone them together.


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## Loop (Jan 8, 2011)

That's cool. I never thought about cutting the funnel. Would it be pretty easy to cut the glass without breaking it? I've never tried cutting any glass before.

One idea I had was to just make something along the lines of this. 










Sorry for the crude drawing, but I was just thinking of using some vinyl tubing again with some sort of cap on the end to hold the fluid in. Not sure if it would work out perfectly, but I was assuming that heating it, bending it, and cooling it would make it keep the "U" shape.


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## Hoppy (Dec 24, 2005)

Loop said:


> That's cool. I never thought about cutting the funnel. Would it be pretty easy to cut the glass without breaking it? I've never tried cutting any glass before.
> 
> One idea I had was to just make something along the lines of this.
> 
> ...


This, or some variation of it, would work well. For example, the loop could be made from a piece of acrylic tube - heat it and bend it - with the vinyl tubing used to join them.

Cutting glass is simple in concept, but takes some practice to do well. Cutting a bottle is very easy, and perhaps not fool proof, but still easy. Cutting the funnel might be a challenge.


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## smannell (Jan 10, 2009)

I got to thinking about some of the various designs suggested here last night when I couldn't sleep, and a couple of important design considerations occurred to me. Provided I'm remembering my various engineering classes properly, using a funnel or flared tubing will not have a significant impact upon the reaction time for a drop checker. Theoretically, it could even slow the reaction down. Second, the diameter of the tubing is not the most important factor in determining the response time. Let me try and explain.

The rate at which a gas dissipates from or is absorbed into a liquid depends upon the following factors.

1. The concentration of the gas present in the liquid (in this case ppm of CO2)
2. The partial pressure of the gas in contact with the liquid
3. The surface area of the liquid(s) in contact with the gas
4. The Reynold's number of the fluids involved (remember that gas is a fluid)
(I'll save this one for last as it is complicated and will only have a small affect)

Item number 1 is what we are trying to measure. For a closed system such as a drop checker, #2 is dependent almost entirely upon #1. Neither of these is affected by the physical design of the drop checker. Item #3 is dependent upon two dimensions: the first is the ID of the top of the tubing (the part in contact with the gas); the second is the ID of the jar minus the OD of the tubing. A funnel at the bottom of the tubing does not impact either of these.

When the drop checker is placed into the tank, CO2 begins to diffuse out of the aquarium water and into the air trapped in the drop checker. The rate at which this occurs depends mostly upon the concentration of the CO2 in the tank and the surface area of the water in contact with the air, ie. the tubing ID. This reaction will continue until the system reaches steady state (equilibrium). The time to reach steady state will depend mostly upon the volume of air trapped in the drop checker. The more air in the system, the more CO2 it can hold at a given temperature/pressure. 

At the same time, CO2 is being absorbed by the indicator fluid from the trapped gases. Once again the rate of this reaction is primarily dependent upon the surface area of the indicator fluid. As before, this will continue until the concentration of the CO2 in the indicator fluid matches that of the aquarium water, assuming that CO2 has the same permeability for both liquids. The total time for this reaction to reach steady sate will depend mostly upon the volume of the indicator solution. 

In simpler terms, in order to get the quickest response time a drop checker should have the following characteristics:

1. Equal areas of indicator fluid and aquarium water in contact with the trapped air.
The smaller of the two areas will be the limiting factor for the rate of gas diffusion.
(This means a bottle with an ID roughly 1.4 times the diameter of the mouth).
2. A large surface area to volume ratio for the indicator fluid.
3. A large surface area to volume ratio for the gas with respect to both liquids.
Essentially you want a short, fat jar with the above diameter to mouth ratio.

Finally, the Reynold's number. For those of you that have never studied any type of fluid mechanics, Reynold's number is a dimensionless number (meaning it has no units such as meters, grams, seconds, etc.) that is used to indicate various properties of moving fluids. It depends upon density, viscosity, flow rate, turbulence, etc. For this application the important factor is the flow/turbulence in the water column of the tubing. The indicator fluid and the trapped gas are essentially motionless, so the only way to speed up the dissipation of CO2 is to get the water in the tubing moving.

Placing a funnel on the end of the tubing might help a tiny bit if it is oriented properly with respect to the water flow in the aquarium. On the other hand, if it is positioned improperly it could impede the flow of water below and therefore inside the tubing. The best way to help increase flow would be to place a "Tee" or "Y" shaped plumbing fixture at the bottom of the tubing, and then turn one end into the flow and the other end away from it. If you are using a "Tee", placing a funnel on the incoming end of the fixture would increase the flow rate through the fixture and thus help stir the water in the vertical section of the tubing. Overall, I'm guessing the water flow is a minor factor in the reaction time compared to the surface areas and volumes involved.

This is probably far more information than anyone wanted to know about a simple drop checker, but that's what happens when an engineer suffers from chronic insomnia. I hope this was in some way helpful (cutting a glass funnel sounds like a pain in the ass). Let me know if you have any questions or couldn't understand my techno-babble.

Sean


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## Loop (Jan 8, 2011)

smannell

Thanks for the fancy tecno-babble.  It was an interesting read. I've never studied anything relating to fluid mechanics before, but alot of the properties your stating are things I had assumed from basic science, but have not yet been able to produce. I've been looking for a container of some sort to design one more like your describing, but I don't think I'm going to find anything like that just sitting in a store somewhere. I'm pretty sure it's something that will have be created for this specific purpose, from scratch, by someone willing to put in more thought/design than most of the companies in this small market want to invest. Even if they did, I'm not sure I would be willing to pay the price they would demand for their investment. Luckily for us financially challenged people there is always a cheap knockoff company waiting to steal designs and sell on ebay for $5. Until that day comes we have Hoppy's design for the best/quickest, and some other easy ones to get by with. 

You're an engineer, why don't you give it a shot at something professionally designed to sell?


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## Hoppy (Dec 24, 2005)

You can experiment with different geometries of drop checkers and if you do you quickly learn that the fastest response time comes from high area of tank water to air bubble surface, low air bubble volume, high area of air bubble to indicator fluid surface, and low volume of indicator fluid. A flared opening like a funnel, does reduce the response time considerably. The biggest effect is having a large surface area to volume ratio for the indicator fluid - a shallow dish of fluid as opposed to a tube of fluid. Reynold's number isn't involved at all. The speed of movement of the dissolved CO2 in water is very high in any case, so much so that it has little effect - you can assume that the CO2 concentration changes instantaneously at any local spot in the tank whenCO2 is added. (It doesn't, but compared to one hour response times, it might as well be instantaneously.)


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## smannell (Jan 10, 2009)

Nice to know someone has actually experimented with these things. Theory and practice don't always coincide. Any idea why the funnel matters when it doesn't change the surface area? Does CO2 tend to rise towards the top of an aquarium (this is something I hadn't considered)? Is it simply causing more water movement in the tubing? I believe you, I'm just trying to figure out the principle involved.

I probably should have simply said water circulation as opposed to Reynold's number since we are dealing with very low flow rates where turbulence is minimal and viscosity doesn't matter (I was simply looking for a term that indicated how much movement was occurring at the gas/liquid interface). My fluid mechanics class was 19 or 20 years ago. If CO2 dissipates that quickly then water circulation probably doesn't matter much at all.

Sean


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## Loop (Jan 8, 2011)

I don't understand why you're saying a funnel doesn't change the surface area. It seems to me it obviously would. Is there something I'm missing here? 

Little opening = small surface area of trapped air to water
Bigger opening = larger surface area of trapped air to water 

Right? Assuming the funnel shape doesn't increase the volume of the trapped air too much that it offsets the gain. 

Unless this is exactly what you mean, that the funnel increases the ratio of air volume to surface area too much. Which I'm definitely too lazy to try and calculate to see.


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## larams67 (Jan 24, 2006)

Loop said:


> I don't understand why you're saying a funnel doesn't change the surface area. It seems to me it obviously would. Is there something I'm missing here?
> 
> Little opening = small surface area of trapped air to water
> Bigger opening = larger surface area of trapped air to water
> ...


The surface area that matters is the area above the ph solution. A funnel shape at the aquarium water side doesn't change that.


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## psalm18.2 (Oct 16, 2010)

What is the "solution" refering to? Is this for ferts?


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## Hoppy (Dec 24, 2005)

That's why the funnel shape is beneficial. The size of the air to DC liquid surface area is also important. The bigger, the better, but the lower the volume of liquid in the DC bulb, the better too.


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## Loop (Jan 8, 2011)

larams67 said:


> The surface area that matters is the area above the ph solution. A funnel shape at the aquarium water side doesn't change that.




I was thinking that both would matter quite a bit. The way I was thinking is that you want CO2 from aquarium water to get to the ph solution. In order for this to happen it needs to get into the trapped air in the drop checker first, and a larger surface area would speed this up. The faster you can get CO2 into that trapped air, the faster CO2 can enter the ph solution, which you would also speed up by having a large surface area. 

I do also see having the least amount of solution and air in there being beneficial. Seems like the lower volume of both, the faster it can reach an equal level of CO2 with the tank water.

I don't mean to sound argumentative about it, I'm just trying to understand the reasoning behind the ideas.


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## Loop (Jan 8, 2011)

psalm18.2 said:


> What is the "solution" refering to? Is this for ferts?


The solution is refering to the liquid inside the drop checker.


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## smannell (Jan 10, 2009)

OK, after looking at your drawing I understand the reason for the confusion. I was assuming that the aquarium water would rise up far enough that it was past the funnel and into the tubing (it's hard to see from the pictures). Obviously this would depend upon the height of the funnel and how far the drop checker was submerged. You are absolutely correct that using a funnel would increase the surface area and decrease the reaction time provided the interface between the trapped air and the tank water was within the funnel as opposed to farther up into the tubing. I apologize for not making my explanation more clear, and sorry if I caused a lot of confusion. Next time I'll try and figure out how to draw picture and include it in the post (worth a thousand words).

I also thought of how to utilize a fat, and hopefully short jar even if it has a large mouth. Provided the jar has a plastic lid that seals well, you could drill a hole the proper size for the tubing (a spade bit works well for this). With a plastic lid and plastic tubing, super glue makes a quick, convenient sealant. I use it for air tubing all the time and never had a leak. If the jar/bottle is too tall, you could try melting candle wax or paraffin and using it to fill the jar part way to decrease the volume of air it would hold. I don't think it would react with or absorb any CO2 (paraffin is used for home made jams and jellies and doesn't affect the taste).

Sean


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## Loop (Jan 8, 2011)

What if you made something shaped like this 










Not sure what you would make it out of, maybe use something like petri dishes and some acrylic tube (the tube would be curved at the top, not square like in the pic). Keep the tubing as short and thin as possible to limit the volume of air. Imagine a more streamlined shape for a finished product. The white square inside the solution would be something that would take up some of the space to keep the solution volume low, but let you keep a large surface area on top of it. You would view it from the angle the red arrow is pointing so that you still had a decent size viewing area with a white background. The shallow squared off shape instead of a funnel should also give less volume of air inside. 

Just an idea that I had trying to think of something that fit the criteria of high surface areas and low volumes.


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## larams67 (Jan 24, 2006)

Loop said:


> What if you made something shaped like this
> 
> 
> 
> ...



The part I'm not sure about is the diameter of the section that connects the surface area chambers. It would seem to restrict the exchange of gases.

I don't see how the chinese made glass styles for instance would be any good. A big funnel reducing down to a pinhole at the bend before opening back up for the ph solution chamber can't be effective.


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## Loop (Jan 8, 2011)

larams67 said:


> The part I'm not sure about is the diameter of the section that connects the surface area chambers. It would seem to restrict the exchange of gases.
> 
> I don't see how the chinese made glass styles for instance would be any good. A big funnel reducing down to a pinhole at the bend before opening back up for the ph solution chamber can't be effective.


I'm not positive about this, but I think that air will exchange gases very easily that it's not a problem. Meaning whatever level of CO2 is in the bottom chamber will quickly equalize with the rest of the trapped air, despite the small opening. Like I said, I'm not positive, but I thought I remember something like that from a science class along time ago.


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## Hoppy (Dec 24, 2005)

If you want the best configuration I have found, here it is: http://www.plantedtank.net/forums/swap-n-shop/133717-fs-magnet-supported-drop-checkers.html There is a DIY thread about how to make it too.


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## btimmer92 (Mar 12, 2011)

The Chinese glass one works great for me. It changes about 4X faster than a DIY one I made..small amount of liquid, and volume, and a decent surface area-comparably. The small diameter at the top doesn't have an effect on the equilibrium speed. It's all about surface areas to liquid volume in the checker.


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## NeocaridinaCollector (Mar 12, 2011)

I'm going to be starting on this tomorrow as was wondering if you could use an old plastic medicine bottle.


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## Loop (Jan 8, 2011)

Traveller said:


> I'm going to be starting on this tomorrow as was wondering if you could use an old plastic medicine bottle.


I don't really know for sure, but I would think it would be fine. I wouldn't think it could be harmful to anything if it's used to hold medicine. Just make sure there's no medicine left in there.


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## Chrome (Feb 26, 2012)

bump for a very useful thread.

I had a brand new airbrush bottle laying around and a few feet of 1 inch OD vinyl tubing. worked great. Just need some solution now.


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## galabar (Oct 19, 2011)

I like the fluval drop check. It seems to have a fairly low internal volume with a large water contact area:

http://ca-en.hagen.com/Aquatic/Watercare/Additives---Supplements/A7551

It also comes with an all-in-one indicator solution for lazy people like me.


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## supergreeneye (Oct 29, 2011)

i will definitely give it a try thanks for the idea


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## haril (Feb 17, 2015)

*Hotel travel shampoo bottle*

Awesomely simple idea to build a drop checker. I am a big DIY fan and I am going to give this a shot. It suddenly occurred to me that the hotels keep these small travel size shampoo and mouthwash bottles which seem to be in the perfect size range so I took home one of those from my official trips. 









They are however plastic and I was wondering if this will effect the test solution or the test itself. I feel it should not since you are using plastic tubing anyway. Any thoughts?

Cheers,
Hari


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