If you don't have a sump be prepared to spend some good money on a decent HOB skimmer. If this doesn't sound like a good option than water changes maybe your best bet, but on a tank that size I would spend the money and invest in a quality hob skimmer. You may also choose to redo the tank and make an overflow. I did this on the 30 gallon in my bedroom, all I did was find an overflow from a broken tank and cut it to fit the corner of the tank. You can do it in an afternoon if your handy and then have a nice, clean looking tank that's drilled and has an overflow. What this really allowed me to do was keep the heater and skimmer under the tank and I used a ER RS-135 for the skimmer, which is a beast and should make the tank run well even with a decent bioload.