I've got a 20-gallon tank with some tetras and a couple of corydoras catfish. I'm trying to figure out if I should do partial water changes weekly or if monthly is enough. Does it depend on whether I have a filter running?
Weekly partial changes of 25-30% are really the way to go for a 20-gallon with that bioload, even with a filter running. A filter handles ammonia conversion but doesn't remove nitrates that build up over time, and your corydoras especially appreciate consistent water quality since they're bottom feeders stirring up detritus.
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