Hi, need to know a bit more about your set up before you could narrow it down to one thing. Ulcers can be a bacterial problem in the water or a secondary infection from a koi with parasites flicking on the side of the pond and then leaving an open wound which can get infected. What fiters and filter media do you have? how often are they cleaned? how often and how much water do you change? do you have an air pump/how much air? etc, normally anywhere where muck and dirt can gather can lead to problems with ulcers etc. Leave your UV on unless a specific treatment needs it off, (mines off this time of year anyway) and leave the filter media in. Hope this helps.
Posted on Oct 7, 2007, 6:23 PM from IP address 82.38.192.15