why do fish tanks need filters but ocean fish don’t require filters?
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Fish in fish tanks live in the same 10/20/50/100 gallons of water. That water will get polluted with their own waste and with algal growth, which needs to be filtered out before the concentration is so high that it hurts the fish (think of living in your own sewage system).
In the ocean, the volume of water is so large that the fish can’t pollute it all that quickly. Additionally, there are other things in the ocean that will naturally “filter” it, like mollusks and other filter feeders. So the ocean will ***usually*** never get so polluted that it becomes toxic. There are cases of algal blooms or human pollution that can certainly damage local wildlife, but those are not the typical conditions for ocean fish.
Size. It’s size, the ocean is stupidly big. Per gallon, oceans have way less fish in them and it’s hard to get a fish tank that isn’t basically polluted. But in order to fully understand, you need to understand how how fish tank filters work.
Contrary to popular belief, the primary filters in fish tanks are biological. Colonies of bacteria break down waste. Plants, algae, plankton and corals absorb waste from the water. For a while, this works fine in aquariums. But you get to the point where there isn’t enough space for these organisms to process all the waste the fish.
What filters do is try to compensate for this lack of space. They provide extra living space for bacteria (that’s what that sponge is actually for) or cultivate algae, or remove waste before it breaks down. They can also use chemicals to remove pollutants from the water.
But this is all to compensate for a lack of space in the tank. If you have a big tank with lots of plants or corals and not many fish, you can get away without a filter (do not attempt this if you don’t know what your doing)
The ocean has plenty of filters. Everything is food for something in the ocean. Fish waste is food for smaller fishes, plants, corals, mollusks, shrimp whatever. Water cycle keeps minerals constantly coming in and rejuvenates o2 levels. Algae growth is kept in check by the huge number of animals that eat it. Everything is constantly recycled in the ocean, but a lack of biodiversity in 90% of aquarium tanks means that human intervention is required to do the job that life and water cycle does in the ocean.
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