I use the 400UV on my 55 gallon, and the 500UV on my 90 gallon. Water is crystal clear in both. The only thing I would caution you about is the elbow joint where the return valve attaches to the spray bar. Mine was loose from day one, and I knew it. Guess my fish bumped it hard one day because they came apart and the filter splashed about 30 gallons of water out of the tank before I caught it.
Aquatop customer service was excellent and the offered me the replacement part, but I fixed it myself with some plumbers tape and a stainless steel hose clamp. It's a deceptively strong filter for how quiet it runs, so make sure the parts fit together tightly.