IMO, that one filter wont be sufficient for all 6 20 gallon tanks. Over filtration is always better than under filtration.
You should also have a protein skimmer running for these tanks.
Also, maroon clowns probably wont do well in such a small tank. Otherwise may object, but i think maroons should be given more space.
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Current setups: 1800 gallon koi pond, 10 gallon planted, 150 gallon reef, other FOWLR tanks
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