# why is it necessary to do weekly 50% water changes?



## nicks7.1985 (Aug 11, 2010)

sorry if thats a silly q to you guys..im new to this. i keep reading on many many posts about doing a 50% weekly water changes if i have high light,fertz,co2 etc... and even to do it with a low light setup i think.

my understanding was that the fish and fertz and co2 provide the nutrients which the plants take up..in the process they take up ammonia and nitrites which r toxic to fish at small levels but the plants use them for nutrients. 

my question is... why do i have to do weekly water changes instead of doing a water change only when my nitrAte levels start getting too high?


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## sean117Ply (Jun 28, 2009)

nicks7.1985 said:


> sorry if thats a silly q to you guys..im new to this. i keep reading on many many posts about doing a 50% weekly water changes if i have high light,fertz,co2 etc... and even to do it with a low light setup i think.
> 
> my understanding was that the fish and fertz and co2 provide the nutrients which the plants take up..in the process they take up ammonia and nitrites which r toxic to fish at small levels but the plants use them for nutrients.
> 
> my question is... why do i have to do weekly water changes instead of doing a water change only when my nitrAte levels start getting too high?


For a planted tank 25% every 1 -2 weeks is sufficient - solely depending on stocking levels of course.

50% water changes is for discus really, and you never use so much fert that the fish suffer.


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## nokturnalkid (Apr 3, 2007)

The reason for wc's is to re-set the nutrients being added to your tank. In different situations, wc's are not a necessity. If you are doing a Walsted style NPT, a wc happens bi-annually if that. With a high light e.i. style tank, nutrients are dosed with excess. I forget the actual numbers but with ei based fert doses and maximum plant uptake, the max of a certain nutrient is 50%(???) of the total dosed for the week. Without a wc and all the excess nutrients, an imbalance may occur which in turns may lead to algae. You do a wc to get all your nutrients back to a known value, which will at or near 0.


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## nicks7.1985 (Aug 11, 2010)

ahh that makes sense nocturnal kid...well im planning to start off with low light but depending on how long its taking the plants to grow i may switch to high.


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## nokturnalkid (Apr 3, 2007)

nicks7.1985 said:


> ahh that makes sense nocturnal kid...well im planning to start off with low light but depending on how long its taking the plants to grow i may switch to high.



In high light tanks, wc are done for acheiving a balance between co2, lights, ferts. If one is out of whack, algae rears it's ugly head. Wc are also done for the fauna in your tank. You can have 60ppm of nitrates with no algae but I dont think your fish will be too happy.

I have 2 low tech tanks with no co2. One gets a 25% wc every week because of shrimps, and another get top offs and a wc maybe every year or so. Plants grow great and no algae. The shrimp tank gets ferts every time I do wc and the other tank gets its ferts from fish poo.


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## Swan900 (Apr 27, 2010)

Actually the w/c is for the build up of unwanted chemicals that are harmful to the fauna such as ammonia, nitrate, etc. Its not to reset the nutrients. I first belived what you did nocturnal kid by in that doing a 50% w/c it would reset the nutirent levels when dosing methods such as EI. But after talking and reading alot with the guys who created it I actually found out its for the fish. Think about it when you dose methods like EI you allready putting excess nutrients into the water, the whole reason of EI and other methods are to put more nutrients in than needed so 'reseting' them as such would be counter-productive.


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## shane3fan (Nov 2, 2009)

Swan900 said:


> Actually the w/c is for the build up of unwanted chemicals that are harmful to the fauna such as ammonia, nitrate, etc. Its not to reset the nutrients. I first belived what you did nocturnal kid by in that doing a 50% w/c it would reset the nutirent levels when dosing methods such as EI. But after talking and reading alot with the guys who created it I actually found out its for the fish. Think about it when you dose methods like EI you allready putting excess nutrients into the water, the whole reason of EI and other methods are to put more nutrients in than needed so 'reseting' them as such would be counter-productive.


 
I have to disagree. Based on what I know about EI, we dose in excess of what we need ( limitless nutrients ) to rule that out as a source of growth concerns. Then, we do a 50% water change to reset the tank. If you dont do the water change and just continue to dose EI there is a good chance that you will build up excess nutrients and cause yourself heartache in many ways. 

In an understocked planted tank with low lights and no EI the water can go a long time without being changed. The plants will use the fish waste as food and the bacteria in the tank will take care of the rest. 

Not an expert---but I did stay at a Holiday Inn one time.


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## RipariumGuy (Aug 6, 2009)

I have to agree with Nocturnalkid and Shane3fan, the 50% water change is to reset the nutrient levels in the aquarium, and also to remove the extra build up of nitrites. Shane3fan covered the whole thing beautifly. 
Regards,
Jake


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## jargonchipmunk (Dec 8, 2008)

the 50% WC is NOT for the fish. For the fish no water changes are needed in heavily planted tanks. The plants are all the nitrate control you'll ever need.

It's to reset the ferts each week so that you don't have to test NPK levels all the time to know (read: estimate) what is in the tank.

Head over to tom's site and read up. In other words, get it from the horse's mouth. barrreport.com


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## Axelrodi202 (Jul 29, 2008)

Actually, in a heavily planted tank, you still need to do water changes. It's to replace certain minerals and trace elements in the water. But a large plant mass does relieve the need for frequent water changes.

And don' worry nicks, the only stupid questions are the ones that go unasked.


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## jargonchipmunk (Dec 8, 2008)

^these elements will be replaced by topoff water if you're using tap.

my low tech tank used to get a change every year just to be sure if that counts.


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## stingraysrule (Apr 4, 2010)

jargonchipmunk said:


> the 50% WC is NOT for the fish. For the fish no water changes are needed in heavily planted tanks. The plants are all the nitrate control you'll ever need.


I would be careful as to what you say. 
IMO, MAYBE you can get away with "no water changes are needed in a heavily planted tank", if you MAYBE, I doubt... had a limited stock of fish. 
People are going to take your words literally, stock up their tank with 
what they think is "heavily" planted, and think they are set. 
An ESTABLISHED planted tank that has been running for at least 12 - 
18 months, using their plants as a "biological" filter takes years to do. 
Anyhow, IMO it is ridiculous not to do any water changes in a tank with something living. Most people in this hobby aren't going to be able to do that cept for maybe Tom Barr and a few others. 
There is no rule as to how many water changes you should do in your tank, planted of otherwise. But, I would say, most would agree that there needs 
to be SOME KIND OF WATER CHANGE, at least to get the bacteria and 
anything else out of the bottom of the substrate that would build up after a years time and not break down.
To answer the original Q to the poster... you don't wait until your ammonia and nitrates are high before you do a water change. You will stress your fish out, and take the chance of disease and death. 
You want to keep your water parameters stable, which IMO will be virtually impossible with no water changes cept for someone besides an "expert", who has unlimited resources with money, time and lots experience. 
Sometimes I wonder if people who are "into" the planted tanks care more about their planted tank, then the living, breathing fish in it.


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## JWA (Feb 17, 2010)

sean117Ply said:


> For a planted tank 25% every 1 -2 weeks is sufficient - solely depending on stocking levels of course.
> 
> 50% water changes is for discus really, and you never use so much fert that the fish suffer.


This is a pretty inaccurate statement.'nough said


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## wendyjo (Feb 20, 2009)

I'm sure the fish appreciate fresh water the same way we appreciate fresh air, and it surely isn't going to hurt them. Plants are nice, but the fish are the creatures that really need to be considered.


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## RipariumGuy (Aug 6, 2009)

wendyjo said:


> I'm sure the fish appreciate fresh water the same way we appreciate fresh air, and it surely isn't going to hurt them. Plants are nice, but the fish are the creatures that really need to be considered.


Yep. I agree. 

In my book, the best thing you can do for your aquarium is a water change. I try and do a weekly 50% water change or a bi-weekly 30%.


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## stingraysrule (Apr 4, 2010)

sean117Ply said:


> For a planted tank 25% every 1 -2 weeks is sufficient - solely depending on stocking levels of course.
> 
> 50% water changes is for discus really, and you never use so much fert that the fish suffer.


As far as I was told most people that have a Discus tank 
DO NOT do water changes 1 x a week. They do water changes 
3 or more times a week. 
IMO 25% water change every other week is not sufficient. 
But, I can't tell you what the right answer is, just as sean117 
cannot either. 
The rule of thumb is 50% water change 1x a week. 
You decide what you want to do. 
It is your tank, yours. 
All people posting on this thread can only give you an opinion. 
It is not an exact science like directions on a box when you put a book shelf together. 
As the months go by and you monitor the progress of your tank 
you will know the answer of how many water changes to do. 
And, I can guarentee it will not be no water changes. 
I do a 10g water change every day out of my 85g stingray tank. 
His poop is so big, I can't stand looking at it.


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## jargonchipmunk (Dec 8, 2008)

I'm fairly certain the question was in regards to the EI method of fertilization. He asked the reasoning behind the 50% WC. Again, it has nothing to do with the fish. Period. It's about fertilizers staying at a non-limiting but controlled level. The fish benefit from the WC's, no doubt, but that's not why he asked. If you're going to add in the fertilizers at the rate EI suggests, the 50% WC is needed. NEEDED. Otherwise, drop the fert rate if you're going to drop the WC rate, as Tom mentions constantly, it's just a suggestion, it can be done many ways, but if you're just starting out, go by the sticky and you'll be better off until you decide how best to fit it to your needs.

(btw, the mention of "not needing" wc was not a suggestion, merely showing two sides of a coin. Yes, it can be done. I had two tanks that had one WC a YEAR and even that was only because I felt impulsive. No I do NOT recommend it when using EI or similar techniques. Is that a better disclaimer? lol )


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## PlantedRich (Jul 21, 2010)

I think of my tank as pretty much the same to my fish as my house is to me. While technically my furnace/AC does keep the air good and clean, I still have to have a day or two where I throw the windows and doors open just to freshen the air. Much the same in tanks, I believe. Got to get some freshness in here someway!!!


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## plantbrain (Dec 15, 2003)

nicks7.1985 said:


> sorry if thats a silly q to you guys..im new to this. i keep reading on many many posts about doing a 50% weekly water changes if i have high light,fertz,co2 etc... and even to do it with a low light setup i think.
> 
> my understanding was that the fish and fertz and co2 provide the nutrients which the plants take up..in the process they take up ammonia and nitrites which r toxic to fish at small levels but the plants use them for nutrients.
> 
> my question is... why do i have to do weekly water changes instead of doing a water change only when my nitrAte levels start getting too high?


Mostly to avoid testing many parameters.....which most folks slack and do not do anyhow. A weekly water change is good for the fish without any plants and keeps not only discus healthy, but all fish.

If we also add plants..........then we can use these water changes to dose ferts and keep them in a stable range for the plants.

The % and frequency can be modified from there by slow reduction+ observation for dosing to suit any tank, or not......up to you.

The issue is that most simply will not test the tank water over time consistently, most will however.......do a regular water change.
It is easier to sweep the floor once a week vs preventing every bit of dirt coming into the house.

Same type of thing.
I do the water changes more for fish than the plants, and to keep the tank clean and tidy.
But........I actually have good sized fish loads.

Regards, 
Tom Barr


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## wearsbunnyslippers (Dec 6, 2007)

we had the same discussion on ukaps a while ago..



wearsbunnyslippers said:


> the ferts you add in EI are to keep you in a ballpark range, the water changes are to reset these values. so without water changes the ferts that are not used up will build and build until you have a brackish water setup. this will very quickly become toxic to plants and fish. excess nutrients cause issues just like too little.





ceg4048 said:


> The fundamental reason for doing a water change is to clean the tank of toxic substances produced by the accelerated metabolism of plants due to their uptake of CO2 and nutrients. These waste products are not only toxic, but they encourage algae as they biodegrade. Not cleaning an EI tank encourages algae due to the excess dirt and organic waste. It also encourages poor fish health. The fact that changing the water also "resets" the nutrient levels is merely a coincidence some find convenient.
> 
> Cheers,





ceg4048 said:


> The proteins, amino acids, fats and carbohydrates that are expelled from the plants during accelerated metabolism become problematic in the confines of the tank. They become part of the biofilm and block access to nutrients/CO2. These products also decay, lowering the oxygen content which have an impact on fauna. The ammonia loading rate is affected in the decay process and the spores of some algal species use this rate as a trigger mechanism. People don't realize how important it is to have a clean tank. When a tank is being setup, there is not enough of these products and so the tank becomes unstable, which triggers algae. When the tank is mature then we have too much of these products which can trigger algae. So yes, absolutely we want to get spores out of the tank with water changes, but fundamentally we want to use the water change to clean the gunk off the surface of the plants, clean the water column of organic pollution and to unload the sediment of built up debris and detritus. People are so freaked out about nutrients that they miss the boat entirely. In a fuel injected tank, keeping it meticulously clean will be the best possible thing you can do for plants and fish.
> 
> While the microbes that perform nitrification do appreciate the products expelled from the plant, the buildup is too much for the plants and animals themselves. With non-CO2 / lean dosing programs, since the nutrient uptake is much slower, the expulsion rate of organic waste is also much slower. The plants adapt to the low nutrient/CO2 rate, become leaner and much more efficient, reducing the waste expulsion even further. It's a much more stable approach as long as the lighting level is not excessive. Enriching CO2 automatically sends the tank into the passing lane of The Autobahn.
> 
> ...





ceg4048 said:


> wearsbunnyslippers said:
> 
> 
> > in terrestrial plants they do secrete some wastes through their roots, but this also server to attract fungus, nitrogen fixing bacteria and to ward off competitors. this is not really classified as excretion.
> ...





wearsbunnyslippers said:


> thats very interesting ceg4048.
> 
> it just goes to show that just because you might understand terrestrial plants doesnt mean that aquatic plants behave the same at all. i have always thought that the water change was pushing the reset button on the fert levels. but what you have explained, and i have confirmed this with a biochemist, opens a whole new door on water changes.
> 
> ...


Cheers,[/quote]


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## wendyjo (Feb 20, 2009)

jargonchipmunk said:


> I'm fairly certain the question was in regards to the EI method of fertilization. He asked the reasoning behind the 50% WC. Again, it has nothing to do with the fish. Period. It's about fertilizers staying at a non-limiting but controlled level. The fish benefit from the WC's, no doubt, but that's not why he asked. If you're going to add in the fertilizers at the rate EI suggests, the 50% WC is needed. NEEDED. Otherwise, drop the fert rate if you're going to drop the WC rate, as Tom mentions constantly, it's just a suggestion, it can be done many ways, but if you're just starting out, go by the sticky and you'll be better off until you decide how best to fit it to your needs.
> 
> (btw, the mention of "not needing" wc was not a suggestion, merely showing two sides of a coin. Yes, it can be done. I had two tanks that had one WC a YEAR and even that was only because I felt impulsive. No I do NOT recommend it when using EI or similar techniques. Is that a better disclaimer? lol )


I didn't take his original post to have to do ONLY with the EI method of fertilization, and going back and reading it again I still don't take it that way. It seemed more of a general question. But you are right that the question was why do 50% WC weekly. And he got a wide range of good answers regarding both plants/ferts AND fish health.


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## nicks7.1985 (Aug 11, 2010)

thank you all for the answers...cleared up a lot of other q's too. right now i only have the aquarium and stand but im going to document the whole process with a few pics as i get more stuff and eventually ill post what the tank looks like. most of the info and lnks iv gotten were from ppl in this forum and i am really grateful


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## herns (May 6, 2008)

jargonchipmunk said:


> It's to reset the ferts each week so that you don't have to test NPK levels all the time to know (read: estimate) what is in the tank.


What test kit should I get when testing NPK levels?


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## nokturnalkid (Apr 3, 2007)

herns said:


> What test kit should I get when testing NPK levels?


Almost any brand test kit will be fine as long as you calibrate the kit to a known value.


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## J.farrand (Jul 12, 2010)

At first with my planted tank I did 25% weekly. I run a canister filter. Now that my water and plants are established I really only do water changes once every three or four weeks. I'm pretty sure the plants are acting like a filter consuming a large part of my nitrogen cycle. This tank I am refering to was my first aquarium. I have to many fish in it. Large bioload. Maybe not perfect but all seems well.


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## plantbrain (Dec 15, 2003)

nokturnalkid said:


> Almost any brand test kit will be fine as long as you calibrate the kit to a known value.


Which is yet another step few hobbyists really bother with, let alone the test kits.

Most run out and start testing with zeal, obsess a few weeks, then the test kit sits for months, or until some other thing else comes along that is a problem.

General day to day, week to week testing is rare among hobbyist. Even if you tell them, nag them, most will not.

Thus the large water change recommendation for most folks, it keeps up on everything and keeps the no# of unknowns way way down........and the technical skills are much less, it's more simple etc.

With more skill and care........not everyone is going to go this route......they can watch and slowly reduce the dosing down progressively and slowly(Patience is also not a trait I associate with most hobbyists either), and then start reducing the water change frequency as well. It's not hard, just takes some time and skill/observation. I still do more than is the bare min needed, just to be on the safe side. Can I get away with less? Sure. But over time, I like the results and the fish are happy.

With less light intensity, they also have more wiggle room dosing etc and water changes. Some of my tanks get once a month water changes, others, weekly. The non CO2 never gets any water changes. Automated water changes are pretty easy and semi automated methods make it simple also, you cannot do automated NO3 and PO4 testing easily.

I think focusing on light and CO2 are more important than dosing or WC's.

Regards, 
Tom Barr


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## J.farrand (Jul 12, 2010)

Tanks for the info Tom


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