Only just started using it myself Mark, picked it up at the HM event. Tried it for a week so only time will tell. Used F90 up until now (liquid) and havent had a problem (that I know of!).
Dilution on F90 is excellent and its pretty dam good on Clearwater too (not as good as F90 though). I had to covert the ounces/gallons into ml though cos my freshwater tank is in ltrs! I put in 25ml per 20ltrs.