To paraphrase a post I read somewhere, if they look like a powder sugar donut, you overdid it. At least with the calcium...I have a tendency to do that, and you'll notice a bunch of dead flies in the bottom of the feeding dish. The powder suffocated them. A little bit of the Ca goes a long way. As for the vitamin powder I use, I have great difficulty getting much to stick on the flies, so quite a bit ends up in their dish (I didn't use a dish at first, but the vitamin piles looked gross and were killing my moss), which they then track all over the glass. I can clean the glass and 24 hours later, it looks like I haven't touched it in a month. I plan on trying a different supplement.