# Water change frequency?



## roadmaster (Nov 5, 2009)

50% weekly water change for last thirty year's.
Maybe twice weekly in tank's with large waste producing fishes or tank's such as my 20 gal currently housing approx forty baby long finned bristlenose and equal number of cherry shrimp.
Tend to stay with what work's for me in my tank's.


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## Fish Em (Jul 3, 2015)

Since I got back into fish keeping, my main motto is when in doubt throw some [water] out. I do changes 25% every other day in my 10 and 20 gallon. My 20 gallon is overstocked a lot, but even if it was stocked to max only, I would still do the same. It is best for me to be in the habit and routine of doing water changes every other day. I don't test the water regularly. Just go by feeling.


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## windelov (May 30, 2015)

i tested my water (pH, NH3, NO2, NO3) every other day for the first month of having my 10 and 30 set up, did water changes according to chems.

Now i do a 50% change on the 10 once a week, and a 33% change on the 30 once a week. Used that month to figure out what frequency the tanks liked


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## goodbytes (Aug 18, 2014)

I don't test my water as the tests can be unreliable and take some of the fun out of the hobby. A lot of people just do 50% once a week which is the safest and most conservative course of action. I do 30% on my 55 and 40% on my 20 gallon tanks. The big tank is understocked though and a larger quantity of water and a lot more filtration than necessary makes the system more stable and requiring less water be changed out. The smaller tanks are nearer to capacity and less water means the system is more quickly polluted so I change more water. Around once a month I do a 50% WC on all tanks just to be sure. Overstocked tanks or particularly dirty fish like Goldfish or Cichlids make 50% twice weekly a prudent course of action unless you're testing the water constantly.


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## Jaxfisher (Jun 2, 2013)

After all, how long would you want to swim in water in an enclosed area that contained your urine & fecal matter? Water changes cannot be done too often!


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## mattinmd (Aug 16, 2014)

A large part of this depends on what kind of fertilizer regime you are using..

A lot of folks here use EI fertilizing methods (or variants thereof) which dictate your water change regime. (typically 50% once a week.. 25% twice a week is not the same, but 30% twice a week is close.)

Side note: a while back I asked a similar question.. Tom Barr (plantbrain)'s commentary is pretty interesting..

http://www.plantedtank.net/forums/showthread.php?t=749945


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## micheljq (Oct 24, 2012)

Hi,

Nitrates are not the sole reason for doing water changes.

If you have algae issues, water changes regularly will help a lot. If your fish population is high, do not hesitate on water changes.

If the water smells fish, even just a little, my reaction is to keep on constant water changes. Is it just me or it seems that my tank goes well when the water smells earth? bad when it smells fish? or it is just a phantasm? Fishes produces toxins, not only nitrates, toxins seems to stay a lot of time in the water, however i am not a scientist by any means.

This only my 2 cents. I must say that i am not a good example, i tend to be lazy on water changes. I keep hitting my head that i must do more, i do more than before and i did lower my fish population lately.

Your nitrates maybe low/look fine, but you can have a fish population issue, overfeeding issue, algae can tell you if it does. Do I make a fixation on algae!? maybe so.

Michel.


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## jcmv4792 (Jul 15, 2015)

Jaxfisher said:


> After all, how long would you want to swim in water in an enclosed area that contained your urine & fecal matter? Water changes cannot be done too often!


If the tank is not overstocked, don't the plants use up the waste as ferts?


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## mattinmd (Aug 16, 2014)

The plants will use up nitrate/ammonia and phosphate from the waste, yes. And certainly those products are some of the the largest outputs of fish waste beyond water and CO2... 

But fish waste contains more than just things that plants can use as fertilizer. Some other stuff gets used by bacteria, which often releases more of the above to plants. Between them, you can go pretty far in terms of breaking down fish waste, assuming the load is light.

However, to break all of it down, you'd need your tank to have a fairly complete ecology... I don't think our tanks can really represent all the cycles that occur in nature to handle waste, just a subset that handles the "bigger issues". 

Can you do without water changes for a long time with the right setup?.. yes..

Would your tank look/grow better with regular water changes?.. probably.

As for fish waste containing toxins... AFAIK, the major toxin in fish waste is ammonia, and our bacteria and plants handle that.. I'm not aware of any other toxins in fish waste that accumulate at a rate that requires water changes on a regular basis.


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## micheljq (Oct 24, 2012)

Sorry toxins maybe was not the right term.

Michel.


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## mattinmd (Aug 16, 2014)

Fair, but pretty much everything else is "mostly harmless"... it would take a long time (months or years) to accumulate enough other waste products to matter, assuming your plants are taking care of all the nitrates/phosphates...


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## micheljq (Oct 24, 2012)

Yes but months is not a long period of time in an aquarium. I am not convinced that everything else which comes from the fauna is mostly harmless, however i have no evidence of it, apart that doing water changes seems to help a lot.

Fishes send bioproducts through their skin/excrements, it can be different if the fish is stressed, or on the mating season. We are still far from knowing all of what is going on in detail in a tank.

Plants are doing the same, allelopathy is one evidence. We know it exists. Allelopathy can be one plant's species trying to be a nuisance to another species, so yet another reason for water changes.

I am not convinced that we do water changes just because of ammonia/nitrites/nitrates, something else seems to be involved. Then we would just test them, and do not touch the tank if they are good, however this is not so simple.

We have biofilters, we check and clean them, we test ammonia and nitrates, they are good, yet we do water changes.

There is the disolved organic matter which is another reason and potential problem and hard to figure out.

Michel.


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## mattinmd (Aug 16, 2014)

I'll forward the hypothesis that if your ammonia/nitrate and phosphate are taken care of, your next problem down the line is going to be TDS or GH increases caused by the "ash" in fish food that your fish are mostly just passing. Those cause osmotic regulation issues, and can eventually kill fish. They're not toxic, but can cause issues, hence "mostly harmless".

If there were substances more hazardous than general TDS/GH affecting ions, I'd suspect that walstad/natural tanks would fail.. but they work, and often they go for several months between water changes if you've got them set up right. 

If there were other hazardous bioproducts, clearly 6 months without a water change should be fatal, right?


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## Mariostg (Sep 6, 2014)

As it stands right now, my dirted sans capped 75 gal is well over 12 months without water change. And it must have been a couple of months since I cleaned the Eheim 2215.

Of course it's not high tech, there is enough of that everywhere else, but the plants grow, the fishes swim, the snails crawl and the shrimps steal food when they can.


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## roadmaster (Nov 5, 2009)

Some are interested in how long one might be able to go without water changes and other's ponder what % might get them buy or be ideal for their particular method.
I tend to favor 50% water changes each week as I have for a long ,long ,time.
Is what I learned work's best for me with fishes, and that is where I began in the hobby with fish only tank's. 
I have also discovered that plants seem to do better for me with the weekly flush and fill.


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