That was my thought as well. I have a 300 gallon tank, to treat the entire tank is expensive when maybe one fish may need it.
Do you keep any small fish in there to keep the cycle going, or do you just put in the sponge as needed?
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My hospital iso just sits half full with a cheapo cascade internal filter. If I need to use it, I just add some mature bio to the filter and drop in a sponge from one of my sumps.
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