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I picked up one of these fluval 13.5 gallon aquariums, and it has a little chamber for filtration on the back. SOMEONE ripped up the default foam block that fits in there, and it got me wondering if I could use some of that modular foam that comes in pelican cases? Or should I just buy the replacement?
I wouldn't use leftover foam, as someone mentioned, you don't know whats been on it, could be dyed or treated in a way you don't want, but absolutely don't buy the replacement either, you can buy filter foam in big sheets and just cut off whatever you need.
Just to illustrate because I assume we're not in the same country, this is what I mean.