I think it would help a lot if we had specifics about your tank:
SPECIFIC water parameters including alkalinity. If they are fine, then take the pat on the back...but you may be overlooking something
Filtration
Live Rock
Inhabitants
Temperature variations
Have you ever checked for stray voltage?
What diet are you using?
Are there any cleaners in use around the place?
The answers to these problems can be tricky. For example, I had customers that would lose fish on Wednesday and Thursday in an office building. Came to find out that they turned the AC off over the weekend....but everything would be looking normal on Monday (temp wise). Fish tend to die of stress a few days after the primary stress was induced (meaning, do not buy fish from the LFS that have not been there at least 72 hours, IMO). Tricky to sort out.
Without having more specifics, there is only so much people can do to help. The point here, though it got a bit off base, is that the cleaner is not the solution to a major ick outbreak. There are few straight treatments for it, BUT, IMO if you have a stress in the tank you will always be fighting this problem.