Question Water Change, How Much Is Correct?

Sokonomi

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This question apparently invokes quite a bit of debate whenever you bring it up, so here we go;

How much and how often should you change the water in your tank?

I'm about to begin my first tank, and I have read that 15 to 20% change is enough,
and you can even skip a week if your water test says everything is fine (never delay more than one week though).
Meanwhile my friend (also about to begin) keeps going off that you need to do at least 50% weekly, no exceptions.
To be clear, we're talking regular maintenance, not the nitrate cycle start.
The parameters are; 20G tank, planted, heated, fully stocked, with some janitor species (kuhli, shrimp).
So please do tell, what ritual do you think is best, and why?
 

Demeter

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If you’ve got a heavy bioload and the nitrates reach over 30 between weekly water changes you should be doing more. Be it more water changes a week or a higher %.

I always do at least 50% every week. Some tanks I do a few a week, some I do daily (fry tanks).
 

Hurricaneharry

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I'm new to fish keeping too
As far as i know 20% max
My first change I did 10%
Parameters all seem good so far on mine ... fingers crossed
Though peeps on here far more experienced than me
 

abarb

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@Hurricaneharry 20% isn’t maximum (it’s even not enough on most tanks). I would say maximum is something like 80%.
I usually do a few 30% water changes or one 50% water change every week. If I have fry then daily or almost daily water changes.
No exact number for every tank.
 

Samanthaljay

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You were correct when you said it can be quite the debate. Everyone does this differently. You just need to find what works for you and your tank. You'll see what I mean once you're months in. As for me, I do weekly 25% water changes, every Sunday, in both my 10 gal and 29 gal tanks. It has just become part of my weekend routine. Saturdays I test my water to see what is going on and almost always my nitrates are only at around 5 but I still change the tank. I personally work better with structure and schedule. I don't want to get in the habit of 'skipping a water change' because my nitrates are still low. Could I skip a week? sure. But this just works for me. Putting new water in the tank has more benefits than just affecting your typical parameter readings.
 

Ed1957

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It all depends on your tanks and the water your replacing it with. My water is terrible so an 80% water change would kill most of the fish. An 80% WC can also change the parameters in your tank to quickly. I recommend a max of 50% and a min of 15%. Fish keeping is not an exact science. You have to find what works for you.
 

Jerome O'Neil

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Whatever is required to keep your nitrates at a reasonable level. If you have a heavily stocked tank, that might be a lot. If your bio-load is low or you have a lot of plants, it might be less.

Measure nitrates before and after a change for a couple of weeks, and plot it on a graph. That will tell you what you need to know.
 

scarface

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It's something you need to figure out for yourself. There's no wrong answer. I say stick with what's most convenient for you. Weekly water change is just a guideline, not an unmalleable rule. But it helps avoid old-tank syndrome down the line.
 

david1978

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I stretch mine out in my current tank but I have a 25 gallon stocking in a 75 gallon tank. I never have an issue with nitrates but I see a trend of my dissolved solids rising and my dissolved oxygen going down along with my kh and ph. Now I don't let it change much but I'm sure the trend would continue if I stretched them farther. So water chemistry is a very complicated thing and you can't go off of nitrates alone.
 

coralbandit

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I change more water then most .
I have 25% marks on my tanks and never change less then 50% and often go up to 80-90%.I would say 75% is average weekly or more often .Not as needed but as often as I can .
I temp match my water perfect and know my parameters don't shift that much in my tanks .I don't give it that much time to do so ! I breed and grow fish so I know water changes are very important and it is known important beyond just levels we test for .
 

TheBettaSushi

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I agree with everyone else. Your water changes should correlate to what works for your tanks needs. If you have high nitrates, change more... if your perameters are good but want to clean debris/uneaten food/fish poo, change less... if you are breeding and have fry, change more often. If your tank requires a lot of water changes then spread them out to twice a week instead of one big massive change, etc.

My tank is only a 6 gallon and I change anywhere between 20-40% depending on my tanks needs. If everything is fine and I just need to replenish my KH, I’ll change about 30%. If I have high nitrates, I’ll change 40% and if I’m just cleaning up, I’ll do 20-25%. This is what works for my tank.
 
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mattgirl

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My motto is "less is best" in everything but water changes.

Fresh clean water is the best medicine on the market. I think of water that hasn't been changed at least once a week being kinda like having to take a bath in the water that has been flushed through a toilet.

Gross, yes it is but that is what your fish are swimming in after a while without a water change. Most illnesses can be prevented by simply keeping the water fresh and clean.

The bio-filtration keeps the ammonia level down but there is more in the water than just ammonia and nitrates. It takes a fair sized water change to make a dent in the dissolved solids in the water.

My big tank gets at the very least 30% of the water changed every 5 or 6 days. Even then I am not sure it is enough so every few weeks it gets a bigger water change. Unfortunately 40 or 50% is about the most I can comfortably do at a time though. The smaller tanks get up to 75% changed each week.
 

TheBettaSushi

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My motto is "less is best" in everything but water changes.

Fresh clean water is the best medicine on the market. I think of water that hasn't been changed at least once a week being kinda like having to take a bath in the water that has been flushed through a toilet.

Gross, yes it is but that is what your fish are swimming in after a while without a water change. Most illnesses can be prevented by simply keeping the water fresh and clean.

The bio-filtration keeps the ammonia level down but there is more in the water than just ammonia and nitrates. It takes a fair sized water change to make a dent in the dissolved solids in the water.

My big tank gets at the very least 30% of the water changed every 5 or 6 days. Even then I am not sure it is enough so every few weeks it gets a bigger water change. Unfortunately 40 or 50% is about the most I can comfortably do at a time though. The smaller tanks get up to 75% changed each week.
That toilet analogy lol!!! That was good. It also depends on your stock too.. I mean if you only have 1 or 2 livestock that don’t make a mess, you can get away with less water changes. But if you have a moderate to heavy bioload, you should be changing more water or changing more frequently... that’s just what I’ve heard.
 
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Sokonomi

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So how about this plan;
Do water changes every sunday, and let nitrate/ammonia levels dictate the percentage.
If you dial it in you can eventually reach a happy equilibrium.

As a sidenote, I will have about half my stock be kuhli loaches (8 to 10), apparently they are pretty lean on the bioload.
 

mattgirl

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That toilet analogy lol!!! That was good. It also depends on your stock too.. I mean if you only have 1 or 2 livestock that don’t make a mess, you can get away with less water changes. But if you have a moderate to heavy bioload, you should be changing more water or changing more frequently... that’s just what I’ve heard. ‍♀
I agree. If there is one Betta in a 10 gallon tank one could go longer or do smaller water changes but even then I truly believe that one little Betta in that much water would still appreciate fresh water a least once a week.

I have seen too many folks coming here wanting to know why their Betta has fin rot. I really believe we would see fewer of those if we all stressed the need for water changes.
So how about this plan;
Do water changes every sunday, and let nitrate/ammonia levels dictate the percentage.
If you dial it in you can eventually reach a happy equilibrium.

As a sidenote, I will have about half my stock be kuhli loaches (8 to 10), apparently they are pretty lean on the bioload.
I always say let your test be your guide but never go longer than once a week between water changes. The test can tell you how much.
 

georgelee1000

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Depends on your stocking and numbers. If your numbers are good, I would keep it <30. If you have a heavily stocked tank with crazy high nitrate. I would do 50% or even 80% water change.
 

aussieJJDude

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I personally do around 80% on my big tank, and around 40 - 50% in my small tank.


I don't really follow my nitrate, since it tends to be low enough anyway due to having my tanks relatively heavily planted. I tend to follow my TDS, which tends to give a rough indication of water quality.

TDS (tap) ~ 30
TDS (65g, 1 week) ~ 100-170
TDS (65g, after waterchange) ~ 60 - 120
TDS (25g, 1 week) ~ 150 - 200
TDS (25g, after waterchange) ~ 100 - 130

My general rule is to keep my big tank below 100, and my smaller tank around 100. This is due to having shrimp, which do appreciate some TDS within the water.
 
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