I've got a 25 watt aqua uv on 20 gallons of the quarantine and a 57 watt on 130 gallons of DT. You should read up on sizing. Aqua UV has a chart on their website. I made sure mine were 90,000 uw/cm2 at my flow rate. It takes power to kill a parasite. If that's your concern, anything less is a waste of money IMO. Good UVs do not come cheap. On the DT mine is on the output of the return pump so all water going back up to the tank goes through it. On the quarantine I use an aquaclear powerhead to send water to the UV and then it just dumps back in the tank on the opposite side. I don't worry about the warning of killing plankton that aqua uv states at this power level. Not a factor for me. I want no parasites making it out of quarantine and the uv on the DT is just insurance incase my quarantine procedures fail. Got tired of constant ich over several years. Happy to say my DT is parasite free.