For the Non-water changers in the crowd. - Tropical Fish Keeping - Aquarium fish care and resources
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post #1 of 104 Old 01-23-2013, 09:36 PM Thread Starter
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For the Non-water changers in the crowd.

I have a question, well, two.

What is the smallest tank that you think can successfully be set up to run with no water changes?

What is the smallest you have run that way, and for how long?

I may have others along the way but let's start with these.

When I first looked at an aquarium, just before Christmas, I asked the LFS guy about running such a setup as you guys do. He gave me that look that you give, unintentionally, to the extremely uninformed. So I am curious.


Total years fish keeping experience: 7 months, can't start counting in years for a while yet.

The shotgun approach to a planted tank with an LED fixture

Small scale nitrogen cycle with a jar, water and fish food; no substrate, filter etc
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post #2 of 104 Old 01-23-2013, 10:30 PM
Sorry to burst your bubble, but humanity has never managed recreating any self-sustaining closed system. Thus trying to maintain a tank with no water changes is going to end poorly for you and the fish. Not even lakes or ponds are entirely closed systems and your trying to recreate something 1/2000 or smaller in scale. The smaller the tank the sooner it is going to crash, that much I can tell you. Freshwater biology is actually MUCH MUCH more complicated then we make it out to be. Really all we ever talk about is the nitrogen cycle, which lets be honest in a aquarium, its not even a complete cycle. Either we do water changes and remove it or some ppl like to insist its complete with the aide of plants, but again lets be honest if you trim back the plants and remove some of the plant matter from the tank again its not complete or self sufficient. There are many many many cycles in a self maintaining system that we completely ignore in a tank. Pretty much one for every element, tho some are more important then others. Nitrogen, phosphate, carbon, sulfate, and ect are a few of the important ones.

The issues with not changing water are this TDS, or total dissolved solids will increase regardless. There is no way to remove TDS apart from water changes or some sort of membrane filter. You can get a TDS meter for $10 off ebay and watch said tank climb and climb and climb. Without water changes certain nutrients like phosphate and sulfates are likely to increase. Carbonates, which buffer your pH are likely to decrease given enough time. Eventually to a point where a pH crash is possible. Most cycles are impossible to complete without some anaerobic step and sufficient anaerobic filtration is pretty much impossible in a aquarium. I've done filterless tanks just fine that consumed all nitrate, but regardless they still got weekly water changes to keep it stable otherwise it would not be long before the plants hit a nutrient deficiency. Some lacking nutrients will simply slow a plant down, some others, like magnesium are vital trace elements for chlorophyll production and photosynthesis.

Fish in such an environment will be fine initially, but after a period of time high TDS or improper water requirements will tax their systems. High enough TDS can chronically harm fish, especially soft water fish which are not built for dealing with it. The signs are slow to appear and irreversible. Lastly the longer between water changes the more the tank water will shift from the tap water which in turn means more or a sudden change for fish when you do change their water. I find it odd some ppl are confused by 50% or more weekly water changes and suggest against it. In reality the tank water in such a tank is more similar to the tap water because so much is changed so often hence when you do change it the fish don't see it as such a huge change since parameters are more similar.

.... I'm probably drunk.

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post #3 of 104 Old 01-24-2013, 02:14 AM
My 15g guppy tank is doing fine without them. It is overstocked but doesn't really affect them(50+ guppies). For some reason the water is balanced and so far I haven't done water changes except for refilling the tank with water because of evaporation. I've had it for over a year.

5g-plant nursery
1g-plant nursery
2g-goldfish tank
1g-snail nursery
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post #4 of 104 Old 01-24-2013, 06:04 AM
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Back in the day, my crowd never did water changes. Just topped off for evaporation. It was a matter of not messing with things. Leave the plants alone or you'll mess up their growth. Leave the fish / water alone or you'll mess up a good environment. Needless to say, we didn't do any testing. Plenty of plants and fat fish equaled a healthy tank. I honestly cannot offer any comparison between those tanks and my current regularly changed tanks. To get back to your original question, the minimum size tank that I can remember being truly healthy at that time was a 15 gallon. I don't even know if they still make those. It was basically a shorter version of the current 20 gallon high.

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post #5 of 104 Old 01-24-2013, 09:04 AM
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The smallest I've done was a 1.5 for 1/2 year. then I moved it's inhabitants to a larger tank and tore it down for an emmersed set up. I usually dont do water changes in my tanks for a month or two... only top ups.

the last time I measured my TDS it was around 140 in my 2.5 gallon, the only inhabitant was a betta and five or 6 cherry shrimps

stocking for the 1.5 was a hoarde of least killifish that kept multiplying (and hence the inevitable tank change)

Last edited by ao; 01-24-2013 at 09:08 AM.
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post #6 of 104 Old 01-24-2013, 02:55 PM
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Mikaila has said it, and said it very well indeed.

If those new members who may not be familiar with our database here would like to follow up, I have two articles in the Freshwater Articles sections that are relevant.

And the article on stress sets out some of the issues that occur from inadequate management.

I'll just make a quick comment on the matter of things being fine can't possibly substantiate this with fact. What may seem fine now, is not fine. And while some fish do seem capable of existing under such conditions, others cannot and will not.


Byron Hosking, BMus, MA
Vancouver, BC, Canada

The aquarist is one who must learn the ways of the biologist, the chemist, and the veterinarian. [unknown source]

Something we all need to remember: The fish you've acquired was quite happy not being owned by you, minding its own business. If you’re going to take it under your wing then you’re responsible for it. Every aspect of its life is under your control, from water quality and temperature to swimming space. [Nathan Hill in PFK]
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post #7 of 104 Old 01-25-2013, 10:05 AM
I agree in the benefit of routine partial water changes to dilute pollution and maintain a healthy water chemistry. This is how nature renews fresh water with rain. I also wish to point out to any newcomers to the hobby that not doing partial water changes weekly may be the short path to failure and fish loss.
However, at least in part, I feel I need to take the middle of the road here.

I'm remembering my youth in the 60's and my mothers tank. She had a 5 gallon, tar sealed, slate bottom Metaframe tank. It had an incandescent tube light in the hood, a bubble up filter with carbon and floss, just enough gravel to cover the bottom. She always had floating plants (Anacharis I think) and there was always a layer of mulm on the bottom. She had a catfish (emerald cory), an anglefish, a pair of red velvet swordtails, some other fish I forget and a (mystery like) snail.
She topped off the tank for evaporation, but never did water changes. The fish in this tank seemed crowded, but were big and healthy and thrived for years.

Not all tanks are created equally. First lets consider or rule out the newer tank not yet cycled and the tanks newer than 6 months not yet established. Weekly water changes in these tanks is even more crucial. Now lets consider smaller tank, the unplanted tank, the over stocked tank, the overfed and/or the poorly maintained tank...
Compare these to the larger, well filtered, heavily planted tanks with a modest stock level.
Or just compare alone the very small tank to the very large tank.
There are so very many variables that affect water quality.
Consider for a moment the commercial aquariums with thousands or millions of gallons of water. Surely they do not do 50% weekly water changes...but they have very sophisticated ($$$) filtration and additive systems that purify and regenerate the water (ensuring sufficient minerals and trace elements).

At the end of the day, the volume and/or frequency of REQUIRED routine partial water changes must be relative to any untreated pollution in the water. In addition, we must replace used nutrients and trace elements lost to fish osmosis and plant usage.
In a larger, well filtered, well planted, established tank, with a modest stock level, this may only be a few gallons a week. In a small, unplanted, overstocked and/or overfed tank, this may mean up to 50% twice a week!

I find myself in a somewhat unique and poor situation with very high nitrates (60-80ppm) in my (country) home well water system. This is most likely the result of a 95 acre farmers field across the road that gets ample amounts of organic (manure) and chemical fertilizer. Larger water changes are simply counter productive for me.
I've experimented with many things to deal with high nitrates and better purify water and plan to write these experiments and experiences in a separate article. However, boiled all down, my greatest success has been tweaking filtration for greater water purity, adding more plants, using additives modestly and reducing weekly water changes to 5g in my 60g tank or about 8.3%. This has been working for me, with crystal clear water for many, many months now and I believe it will continue to be even more successful into the future.

Finally, some have suggested that the aquarium is a closed system that can't be managed as well as nature. Although I agree that we may be missing some key life forms that would [even] better purify water, we also don't have torrential rains that that muddy the water or runoff from agriculture, landfills and chemical plants, etc. Instead, we have a lab experiment where we can control the inputs and strive for very pure, healthy water chemistry.

Disclaimer: For the average aquarium, in addition to sound tank/filter maintenance and proper feeding, I simply must recommend a 25% to 50% weekly water change as the best way to ensure a healthy, consistent water chemistry for your fish.
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post #8 of 104 Old 01-25-2013, 10:58 AM
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wheres bealsbob on this thread?
I'm calling you out....
AS you are the one man i see saying ''dont change the water'' all the time..... you'd think you had an opinion here surely?
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post #9 of 104 Old 01-25-2013, 11:02 AM Thread Starter
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Originally Posted by AbbeysDad View Post
For the average aquarium, in addition to sound tank/filter maintenance and proper feeding, I simply must recommend a 25% to 50% weekly water change as the best way to ensure a healthy, consistent water chemistry for your fish.
This is the crux of the whole thing, the average aquarium is probably better than 95% of aquariums out there which makes the need for partial water change the norm. Any of us who are actually doing no changes or are even looking at the idea, however remote the actual implementation of the idea is (I probably won't try it), are going to be in the 5% or less of fish keepers.

I'm one of the curious ones and like to see and learn what others are doing that is not the norm. Whether I condone, agree, or disagree with it has no bearing on my level of curiosity.


Total years fish keeping experience: 7 months, can't start counting in years for a while yet.

The shotgun approach to a planted tank with an LED fixture

Small scale nitrogen cycle with a jar, water and fish food; no substrate, filter etc
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post #10 of 104 Old 01-25-2013, 11:31 AM
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Dunno, Jeff. . . I suppose it all depends on how you look at things, really. The average aquarium HERE, on THIS forum, and among fish heads like US. . . does tend to get it's weekly water change. We understand the effects, more or less, on the inhabitants and the system as a whole if we fail to take proper care of our fish, and we LIKE our fish, and do our best to give them proper care.

That said, I know entirely too many people here in the 'real' world that have fish tanks. And it seems to me, at least in my area, that fish aren't so much regarded as animals or pets, so much as a decoration - like a picture in a frame or a vase of flowers. MOST of the people I know that have aquariums DO NOT change the water, EVER. And when/if they do, they almost always do it in such a way as to cause a full-tank cycle - and they never even seem to notice.

So in my PERSONAL experience, I'd say that the majority of people who keep fish do NOT do regular water changes. And while I don't think it is in any way the proper way of taking care of the wetpets, somehow. . . somehow they all manage to continue to have living fish! I don't understand it, but there it is. And no matter how much I talk to them and try to convince them - it doesn't work, because their fish are 'just fine' after all of these years. *shrugs* Fish can adapt to anything given time. And they might not live as long as they could have, but they manage somehow. . .

MY fish, on the other hand, are used to clean, fresh water. And if I were to stop doing water changes, I'm quite sure they'd die. . . I remember when I first started keeping fish - I didn't do research, and I did things wrong entirely. ALL of these people told me the same thing. "When you bring home fish, some of them die - it's just the way it is. The ones that live will be fine, though..." I refused to believe that people would buy a pet with the knowledge that it'd probably die, and that's how I found this site. If I wanted to buy 3 kittens, and was told that 2 wouldn't make it. . . I don't think I'd keep cats. Same goes for fish...

*sorry, random...*
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