well, like we all said, a sponge wouldnt provide adequate filtration for a 55... if its all you got, its better than nothing, but a cheap hob
from walmart would do the trick... check craigslist... i found a guy here, im going tomorrow to get the filters, all the stuff listed for $35 (talked him down some
) and basically all it needs is a $5 part from fluval to make it work (impeller)... you can get canisters very cheap used, like a quarter what they cost new... now with your ph at 7.4, imo
you can keep about any fish you want (maybe not discus) because its fairly neutral... mine stays at 7.6-7.8, thats straight from the tap, and i have cichlids, neons, guppies, balas, tinfoils, and a bunch of others and they are all doing very well, all at the same ph... ph isnt really that big of a factor in what you can keep unless you get in to the delicate fish like discus where they do need a low ph... good luck at the yard sales tomorrow (i just cant call it today, i havent went to sleep yet
), im going to hit a few myself (for baby stuff)...