180-230gph is good. A canister of 320gph packed with media will push out about 230-250gph. The key is to give enough time for the UV penetrate and kill microbes as it's exposed to the light.selki;2194260; said:if anything id have to place it on the side of tank.
or on top.
not too sure, around 100 something but i read somewhere up to 400gal? I doubt it.
how many GPH do u recommend on a 18w??