Originally Posted by raun

Its been a while since I've had to deal with fish sicknesses, but if I remember correctly ick is usually caused by stress. That can be from changing tanks, or an underlaying sickness. A UV light will help kill parasites and bacteria in the water column, but if your fish already have something the UV won't help much; it will help to prevent the spreading of what ever caused the problem to the other fish, though.

If your fish only have ick, it tends to go away by itself if the tank is stable, and you're less likely to spread it to other fish if the tank is stable.

Treating a 125 gallon tank is expensive. I'd recommend pulling out the sick fish, and do a ick treatment and maybe a bacterial infection treatment. Going out and buying a 5 or 10 gallon tank for treatment is probably cheaper than treating your 125. Even a 2 gallon plastic "critter keeper" will work. I like the Jungle ick clear tablets. They've always worked for me in the past. I treat my planted tanks directly as a last resort.

I have a 5watt UV on my 75 gallon, which is usually off. This is probably too small, but when I started this tank a year ago it fixed my initial baterial bloom, that wouldn't go away by it self for 3 weeks, in under 72 hours. Your 24 watter sounds fine to me.