I have a 20G Long tank that has a terta 30-60 (cycles 300 GPH) on it already, but it has a senegal bichir, oscar and red devil in it.. I have a spare 20G tetra filter laying in my closet. should i use it too?
IMO, get the correct media for each one when you can, but if you just want to throw the old one on now so it can start getting BB, just throw in whatever sterile sponge or filter media you have. If the HOB is clean, it should just move water & grow BB.