I've currently have a 55 gallon cycling im using 2 aqua tech 30-60 hob filters, one of which i took off my well established 30 gallon tropical tank. ( i decided to give all the fish in the 30 to friend who just finished cycling his own 45 gallon tank so i could use the filter to speed up the cycling process on my 55gallon. Now! Before anyone says anything i know that oscars arnt ment to go in a 55 gallon but im buying my oscars small around 2.5 inches and will use the 55gallon for growing them out till i get my grandfathers 125 gallon in November after all his estate matters are settled.