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So, I just took a nice long shower and had a thought that many of you have probably had. To keep my question simple- why don't lakes, rivers, or the ocean ever need water changes? So obviously my first thought was "well rain brings fresh water to every water source and nearly every river/ocean is connected. But only pure water is evaporated! Everything else stays behind in the water. Now... Just like in aquariums, we have to do water changes to keep our nitrates and everything else in check, but I don't understand why lakes, rivers and oceans (mainly lakes) don't need this done. Are there microorganisms that simply transform nitrates into something else? Or are there just enough aquadic plants and filter feeders in the wild that keep the nitrates low enough to sustain life? If that's not the answer I would be completely baffled but I would love to hear someone's opinion that has had this same thought as me pr someone who has the answer.
 

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My wife and I were talking about this the other day. She didn't understand the need for the constant water changes and we figured the rain and flow of streams and the volume of water in lakes is the difference. Plus a tank is a closed system where even a lake has water coming in and out.

It'd be interesting to test the water in a lake.

I've kept fish for 40 years, and I never did weekly water changes and always had healthy fish- if they are breeding doesn't that mean conditions are good? A water change was topping off the tank when it evaporated, and the occasional cleaning of the gravel in the under gravel filter system where you'd siphon out maybe 1/3 of the tank.
Right now my daughter has a 10 gallon tank with a big angelfish (it's probably 5" and was an inch when she got it a year ago), a 5-6" bristlenose pleco, a 3" cory and a couple 2" goldfish that were feeders for this big albino frog she has in another tank. All of those fish are doing well and she never does a water change, just fills it up every couple weeks when the level drops a couple inches. That goes against every piece of advice you get- tank too small for the fish, not enough water changes etc. The water chemistry is perfect- it's never been tested until recently, when I got my new test kit and was curious, and it's fine.
 

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Put me down as one that does not buy into all the water changes. I vacuum the substrate and do a water change about every 6 months, clean the filters every 2 to 3 months. Our fish are doing great and have been for a long time. I believe the more a fish keeper stays out of a tank the better the overall health of that tank is. I see a lot of people complain about parasites, bacterial and fungal diseases and how having great water quality is the single best way to combat these. I do not have these problems, so I'm not quite sure what to think of this.
There are a lot of bodies of water with no creeks ,rivers or springs feeding them, the fish do great in these.
 

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Large amounts of algae and plants (and plankton in the ocean). Also most bodies of water connect to a ground water system, where the water is carried out and more nitrates are remove via all the plants/trees on land. So yeah, unless you have a very heavily planted tank or you have a ton of algae growth, that's why water changes are necessary.
 

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Isn't the ratio between total water volume to waste producing animals a factor? My 18 fish in a 75 gallon tank doesn't exactly mimic the natural conditions that mbuna are found in.
 

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morrismorris said:
Isn't the ratio between total water volume to waste producing animals a factor?
Well yeah, but do any of our fish actually make a living or are they fed by us?
An aquarium is a drop of water. The equivalent of food that is dumped into an aquarium is probably trillions of tons dumped into a big lake every day. The amount of Nitrogen in natural waters is generally a fixed amount (unless ther is agricultural run off).
Something goes in, something should go out. That many cichlids are hardy and can survival well in poor water conditions does not mean they won't do better in more favorable water conditions. The more water is changed the better off most fish in captivity are.
 

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BC in SK said:
morrismorris said:
Isn't the ratio between total water volume to waste producing animals a factor?
Well yeah, but do any of our fish actually make a living or are they fed by us?
An aquarium is a drop of water. The equivalent of food that is dumped into an aquarium is probably trillions of tons dumped into a big lake every day. The amount of Nitrogen in natural waters is generally a fixed amount (unless ther is agricultural run off).
Something goes in, something should go out. That many cichlids are hardy and can survival well in poor water conditions does not mean they won't do better in more favorable water conditions. The more water is changed the better off most fish in captivity are.
You have good points. Over feeding is a big killer.
 
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