BH90 filling too quickly

Have had my BH90 for about 6 months and am mostly pleased so far. Running it on a 60g mixed reef tank (recently upgraded from a 55g). For the last month or so, it's pulling very, very thin skim, mostly water, and the collection cup is filling up very quickly (less than 15 minutes). It was doing this even before I switched it to the new tank. I have to have someone sitting there watching it when it runs to make sure it doesn't overflow.

Thoughts?