I personally would use an aqua clear power filter. It's not the best, but IMHO it's the best power filter available and the best would be a skimmer+power heads and a mechanical filter, which is VERY overkill and unnesisary and the fish are only staying in there for approx. a month in most cases. I would advise against a UGF, as you have to use gravel for UGF's and substrate, rocks, etc. will make life easier for ich and similar parasites, which IS NOT something you want to do.