Check online for reviews that tell you what they're rated for, but I believe the regular AquaC is probably up to at least 70-80 gallons anyway. The Pro may get you above 100, but would be overkill for anything near 50 gallons. If anybody is interested, there is a local guy selling a regular AquaC for around $100, maybe a little less. Please let me know if you are interested and I can check into it.