Watts is what you want to look at. The GPH
or flow rate is just the rate you need to have the water pass through the light to get maximum kill rate.
Shop around because some 25 watt lights are rated for a 125 and others are not.
I had a aqua ultraviolet with the wiper cleaner thingy... I do not like the wiper thingy because it always leaked after I used it. The rest of the light was good.