Invest in a pond uv sterilizer. I had the same problem in my 125g years ago, eventually the water turned pee green and couldn't see the fish. I now have uv lights on my 2 bigger tanks, and worry free. Haven't had to treat for ICK since before the uv, and I've brought home many new guys since then. I haven't seen cloudy/hazey water since then, or unless I'm cycling a new tank
I wouldn't buy the uv light built in a filter already. The flow rate needs to be slow to zap the particles. I use a 5wt uv light (for ponds) with a aquaclear powerhead for 40-70g. The uv light is screwed underneath the tanks in the stand. Makes it easier. I have the same set up in the 265g and 125g. 5 watt is all you need. Replacement bulbs are $25 each, change them yearly.
Do NOT use algae destroyer or anything. Learned the hard way before getting the uv lights the meds can cause liver failure. One by one over a couple months I lost almost all my fish in what seemed to be out of nowhere. Then the owner at my lfs told me why...