# to cover or not



## alphabeta (Jul 14, 2014)

Just a general question.
some people use a top cover for the tank, usually that came with the tank. some people keep the tank open. 

any reasons for one or another, besides: 
pros covered tank: less evaporation, fish will not fly out of the tank, protect the light from water especially if the light is close to the water, ?
pros not to cover: more light gets into tank (condensation will obscure some light), enjoy the tank from the top view, ? 

any impact on CO2 or O2? or any other important factors for plants or/and fish? 

Just curious.


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## Seattle_Aquarist (Jun 15, 2008)

Hi alphabeta,

You summed up the major reason as to why and why not have a glass top. I use them because I have lost fish from jumping and I don't like to have to fill my tank more than once a week.

As for the loss of light; I did some tests to quantify the amount of loss using our club PAR meter. I used my standard 30 gallon (36" length) with an 2X36 watt (6700K) AH Supply kit over a Aqueon Versa-Top. With new bulbs in the fixture and no glass top the PAR = 110; with "dirty"* Versa-Top in place PAR = 96; with cleaned Versa-Top in place PAR = 101. All readings were taken at the substrate level about 13 inches below the fixture.

dirty* = lots of dried water spots on top, condensation; dust

So in answer to quantify the response it does block light; a dirty* glass top reduces light by about 13%; a clean glass top reduces it by about 8%.....not a much as some might think.


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## sohankpatel (Jul 10, 2015)

I personally decided to go lidless. For 2 reasons, i dont have enough money to afford a glass top , and i dont really keep fish that are known for jumping


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## alphabeta (Jul 14, 2014)

@Seattle_Aquarist thanks! interesting and very useful actually to have some PAR numbers on that. indeed, ~10% loss is not a big loss. 

I am still interested regarding O2. Probably i am overthinking it, but if the water is to the top, say 1/2"-3/4" to the glass, and the glass covers the tank very well, with little room at the edges. Does that impact how much O2 is dissolved actually in water from the current rips of the filter? Can that create O2 deficiency for the fish, while CO2 is run at 25-30ppm? How that squares?


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## BBradbury (Nov 8, 2010)

*Tank Covers or No*

Hello alph...

I have both covered and uncovered tanks. If you have fish that tend to be jumpers, then you've got to keep the tank covered. i have emersed plants in some tanks and the leaves must be out of the water for them to grow properly. I have these uncovered to allow the leaves to grow above the tank. Either way, I don't think CO2 is affected. It's in the surrounding air and in the dissolved fish and plant wastes and this seems to provide enough nutrients for my plants. 

Your call.

B


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## Maverick2015 (Aug 8, 2015)

There is a difference with gas exchange as well. I can't say for sure what the difference is with added CO2 since I run low tech. But since I am low tech I don't run a glass lid. Plus I like the look and don't feel like buying one. A canopy might be another way to go as it won't block the light but keeps the jumpers in place. Also, some people use egg crate for jumpers but it does block some light as well.


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## rtfish (Oct 2, 2014)

I have hatchets and eels and four little kids that throw things.... I have a versa top with the black rubber strip removed


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## g4search (Aug 10, 2014)

*cover vs non-cover*



alphabeta said:


> I am still interested regarding O2. Probably i am overthinking it, but if the water is to the top, say 1/2"-3/4" to the glass, and the glass covers the tank very well, with little room at the edges. Does that impact how much O2 is dissolved actually in water from the current rips of the filter? Can that create O2 deficiency for the fish, while CO2 is run at 25-30ppm? How that squares?



alphabeta,

Your question regarding O2 is really important and you are not overthinking it !!

When you have a tightly covered tank with little room at the edges, you essentially have a CLOSED system! Under these conditions Henry's law has to be applied when it comes to estimating the amount of dissolved gasses in the tank.
[*Henry's law* states: "At a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid."]

This means, if you sparge a single gas (in your case CO2) into a CLOSED Tank system, this gas will eventually replace all other gases in that system. In other words, given enough time CO2 will drive O2 out of your tank (not just oxygen, but nitrogen too). Consequently, your fish will suffocate due to the lack of O2. [NOT due to the presence of CO2]

However, in the planted tank things are somewhat different. As long as the light is on, the plants photosynthesize and produce ample of O2 _in situ_, so your fish have enough O2 to breathe (min. of 4 ppm is needed). 

I want to emphasize that the danger of driving O2 out of your tank ONLY exists for the CLOSED system. If your tank is OPEN, the gasses (over the water column) mix so fast with the surrounding air that you can no longer drive O2 out of your tank i.e. below critical levels. 

THIS IS THE MOST IMPORTANT DIFFERENCE between an OPEN and glass COVERED (CLOSED) aquarium!


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## essabee (Oct 7, 2006)

I cannot say on which side you all think I belong in this discussion - I personally place myself with the advocates of the open tank though all and each of my tanks (all planted) are completely enclosed by canopies on the top.

The inside of all the canopies have good reflective surfaces and are water resistant. The canopy houses the lights and to prevent condensation and accumulation of heat are provided with ventilation and exhaust (air extraction) fans. There are no glass sheets or any other transparent barrier between the canopy and the tank's water surface. The canopy will prevent attempts of escape by even the best jumpers as there are no gaps and all the air ducts have 5mm screens.

Technically speaking my tanks are covered, I have hatches through which I feed the tank and do the necessary chores. I appear to have the best of both the worlds.

I did not consciously hatch upon this canopy system. My first tank was a birthday gift from my parents more than 50 years ago - that tank had a double sloping shed type canopy with an incandescent bulb; and wire meshed ventilator spaces on its 2 triangular sides; and a small hatch opening on one of its sloped roof for feeding. That tank was a 2'X1'X1.25' tank with sheet metal frame and base. As I grew more ambitious I started building bigger tanks for myself and stuck to the same basic model. The town we lived in did not have any aquarium shop those days - in fact I believe my little tank was the first for that town. Over the years my canopies only got a little more sophisticated but has the same basic features.


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## Freemananana (Jan 2, 2015)

I use lids to keep the moisture (evaporation) down in the canopy AND under my stand since I have a sump. With 8' of open top tank, I'm sure I'd be loosing too much water to evaporation. Right now, I lose about an inch or so from my sump (55 gallon tank) every week. 

I also want to mention children and pets. I have both. Well, not to mention I'm known for tossing things when I play with my daughter. A lid is a great safety net so that Doc McStuffins doesn't go for a swim with the fishes.


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## Bushkill (Feb 15, 2012)

Running close to 30 tanks and in the area of 1,000G of water, I'll just say that I only keep a few of them topless and that's largely determined by plants and inhabitants. The large majority are glass-covered and they are DIY's with glass that's scavenged from broken or Petco cheapo tanks. The glass tops do not go edge to edge and simply serve to at least limit evaporation and contain splashing from filters, not eliminate it. Even the glass tops aren't 100% "jumper-safe". I've had fish squirt through the 1/4" gap in the back of some tanks that allows the heater cord through. Lastly, glass tops that are a little thicker than versa tops gives me a safe place to rest fish food containers, and just as conveniently a safe place for my coffee cup.


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## loach guy (Jun 2, 2014)

I currently have my 75 gallon uncovered. I run into over-heating issues. Removing the lids keeps this to a minimum.

g4search: I had learned differently. That adding CO2 to the water column is exactly that. Adding CO2 does not remove any molecules, it just adds to it. So I'm not sure about the driving O2 off. Since I doubt anyone plans on adding CO2 to their system without plants, I suppose it's a moot point anyway.


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## alphabeta (Jul 14, 2014)

thanks All for sharing the info. Useful and instructive. Looks like there is no one solution, as expected, but looks like having some open area while covering with glass is recommended. 
@g4search very interesting, and backs up what i had at intuitive level.


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## Raymond S. (Dec 29, 2012)

I do regular 50% water changes and loose less water if there is a top. I'd rather not
top off mid week. Sure it depends on the humidity level where you live. But TDS changes with top off's if you don't use dist. or R/O water for it. But I use an air stone to power my filter so that adds to evaporation. 
I do get a glass place to cut a glass top for me that is short by 1" on each end for access. Heater line/air line/feeding. Cleans easier and doesn't have that strip.


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## TekWarren (Oct 6, 2013)

I usually end up using a lid depending on the time of year it is. In the summer I don't use a lid but in the winter when the air in the house gets dry and I start noticing a lot of evap...that's when I'll put the lid on.


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## end3r.P (Aug 31, 2015)

rtfish said:


> I have hatchets and eels and four little kids that throw things.... I have a versa top with the black rubber strip removed


You can remove the rubber strip!? Can you just pull it off? I guess that leaves you with two pieces of glass? Perhaps these are dumb questions, but I never thought to just take it apart... I hate that strip.


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## klibs (May 1, 2014)

The only tank I keep a cover on is my QT tank and that is only because the cat could get into that one. My other 2 tanks are lidless - it's better that way IMO

Some more pros of not having a cover:

They get dirty and need to be cleaned
Constantly have to move them when you need to get in the tank
Generally they are a PITA

And yes - you should be able to remove the rubber strip that connects the two pieces of any cover


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## rtfish (Oct 2, 2014)

end3r.P said:


> You can remove the rubber strip!? Can you just pull it off? I guess that leaves you with two pieces of glass? Perhaps these are dumb questions, but I never thought to just take it apart... I hate that strip.


Yep. I started with a razor blade pushing it in the seem, but then realized I could just pull it off after a corner just pulled away with a bit of force. It does leave you with two separate pieces. I push one all the way back and one all the way forward so there is a 1 inch gap or so between the two which works out nicely as that puts the gap almost directly over my floaters which were getting light blocked from the strip. You do have to be a bit more careful with pushing and pulling the two pieces of glass, but I've not had problems with it.


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## g4search (Aug 10, 2014)

loach guy said:


> g4search: I had learned differently. That adding CO2 to the water column is exactly that. Adding CO2 does not remove any molecules, it just adds to it. So I'm not sure about the driving O2 off. Since I doubt anyone plans on adding CO2 to their system without plants, I suppose it's a moot point anyway.



loach guy,

when you take a cup of carbonated water and pour it into your tank, then you are right, you ADD CO2 to the water column. Nothing else happens.

However, when you constantly bubble a gas (e.g. CO2) into a CLOSED tank, then you not only add, but you also replace the entire air (gas) over the water column with the gas (CO2) you are adding. Since the oxygen in the air is being replaced by the gas and the oxygen in the air is in equilibrium with the dissolved oxygen in the water, you are also driving off the oxygen (and other gasses) in the water. 

Again, this is ONLY applicable to a CLOSED system.


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## loach guy (Jun 2, 2014)

g4search said:


> loach guy,
> 
> when you take a cup of carbonated water and pour it into your tank, then you are right, you ADD CO2 to the water column. Nothing else happens.
> 
> ...


I see. So you were referencing a theoretical sealed volume of water, not an aquarium. even in this scenario, I am still not seeing how adding CO2 replaces oxygen in water or air. The oxygen didn't go anywhere. There would just be more CO2, and a higher pressure than ambient.


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## g4search (Aug 10, 2014)

loach guy said:


> I see. So you were referencing a theoretical sealed volume of water, not an aquarium. even in this scenario, I am still not seeing how adding CO2 replaces oxygen in water or air. The oxygen didn't go anywhere. There would just be more CO2, and a higher pressure than ambient.



Hey loach guy,
a sealed tank is a completely different beast. Sealed means nothing goes in or out. 

A CLOSED system on the other hand is a tank with a tight-fitting lid (usually glass or plastic cover) that severely restricts the free flow of air.
Look at the lid as a check valve! It allows the (slightly pressurized) air underneath the cover to leave, but it does not allow it back in. When you now bubble CO2 into this system, the air above the water column is slowly being replaced by the incoming CO2 gas. Once the air is gone, the oxygen is gone! It's that simple.


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## essabee (Oct 7, 2006)

loach guy said:


> I see. So you were referencing a theoretical sealed volume of water, not an aquarium. even in this scenario, I am still not seeing how adding CO2 replaces oxygen in water or air. The oxygen didn't go anywhere. There would just be more CO2, and a higher pressure than ambient.


Just imagine that the CO2 addition is the exhaust of a running car and covering the tank was closing the garage door with the car inside. If the garage is ill-ventilated would not the oxygen get depleted.

Tight fitting covers would do just that in tanks that are enriched with CO2. 

Initially CO2 escapes from the tank water (which has higher than equilibrium level of CO2) to make the air above in equilibrium with the tank atmosphere. This process will continue as long as air above the tank is not in equilibrium with the tank. 

If the ventilation of the air above the tank is seriously impaired then at lights off (photosynthesis off) time the air above the tank is more CO2 rich than normal atmospheric air. At night the respiration will further decrease O2 and increase CO2 - this is not driving out merely replacement and dis-balance.


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## loach guy (Jun 2, 2014)

g4search said:


> Hey loach guy,
> a sealed tank is a completely different beast. Sealed means nothing goes in or out.
> 
> A CLOSED system on the other hand is a tank with a tight-fitting lid (usually glass or plastic cover) that severely restricts the free flow of air.
> Look at the lid as a check valve! It allows the (slightly pressurized) air underneath the cover to leave, but it does not allow it back in. When you now bubble CO2 into this system, the air above the water column is slowly being replaced by the incoming CO2 gas. Once the air is gone, the oxygen is gone! It's that simple.


I am picking up what you're laying down. Although as you said, the plants create O2 offsetting this effect. It's pretty cool how much science is going on in these tanks.


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## Soxfandowd (Aug 1, 2014)

rtfish said:


> Yep. I started with a razor blade pushing it in the seem, but then realized I could just pull it off after a corner just pulled away with a bit of force. It does leave you with two separate pieces. I push one all the way back and one all the way forward so there is a 1 inch gap or so between the two which works out nicely as that puts the gap almost directly over my floaters which were getting light blocked from the strip. You do have to be a bit more careful with pushing and pulling the two pieces of glass, but I've not had problems with it.


If they just made that hinge using clear plastic I wouldn't mind it. I like having the hinge to open the top but hate that black, light blocking strip down the center of my tank.


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## whitepapagold (Aug 19, 2010)

Im an "acrylic tank (uniquarium), covered openings, SS mesh over filter intakes, canopy" type of guy. If it can be covered, I cover it.

The topless glass ADA tanks are beyond me- you see all the equipment, the glare from the light and the hanging light itself. Yet they are by far the most popular... I like to maintain a stronger "suspension of disbelief".

I prefer a framed look free of ANY equipment. The only thing you see on my 125G is the output nozzle on the right- and you can barely see that. Even lily pipes look bad to me.

As far as covered goes- I converted my ADA 60F into a drinking bowl for my cat. When I did, I found SO MANY dried up fish, shrimp and snails it was ridiculous... I knew a bunch got out but this was ridiculous... Soooo many snails and shrimp...

I could care less about a little par loss, and I rarely clean my tops- water marks everywhere... But killing animals is where I draw the line. Its like the apple factory with the suicide net around it (yes thats 100% real)... You can't stop them from jumping! I needed a suicide net for my 60F.


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## alphabeta (Jul 14, 2014)

thank you guys all. amazing how many facets this hobby has. 
i definitely learned more than i expected when put the question.


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## rtfish (Oct 2, 2014)

alphabeta said:


> thank you guys all. amazing how many facets this hobby has.
> i definitely learned more than i expected when put the question.


Something else to note, be careful where you put the lid when working on the tank. I am now running a topless tank.....


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## Bushkill (Feb 15, 2012)

whitepapagold said:


> You can't stop them from jumping! I needed a suicide net for my 60F.


 That's my good laugh for the day and early too!


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## BrentB (Dec 4, 2014)

TekWarren said:


> I usually end up using a lid depending on the time of year it is. In the summer I don't use a lid but in the winter when the air in the house gets dry and I start noticing a lot of evap...that's when I'll put the lid on.


i do the same off most of spring summer and fall on in the winter helps hold the heat in and in the dry winter air the evap is worse.

Brent


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## alphabeta (Jul 14, 2014)

rtfish said:


> Something else to note, be careful where you put the lid when working on the tank. I am now running a topless tank.....


i hear you . I do have a routine for that. Vertical with a bucket cover underneath, against the tank or the wall, with a towel or something between the tank/wall and lid. laying it around is a no, no.


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## Aplomado (Feb 20, 2013)

Do it.

Then your fish won't kill themselves and you won't have to constantly add new water.


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## rtfish (Oct 2, 2014)

alphabeta said:


> i hear you . I do have a routine for that. Vertical with a bucket cover underneath, against the tank or the wall, with a towel or something between the tank/wall and lid. laying it around is a no, no.


 I didn't tuck it in far enough on the side of my tank. Trimming floaters and moving left to right. Wasn't looking down as I moved and my knee pushed the pane over like a falling domino. Splat and shatter! Luckily local petco has the 38x18 in stock.


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