Diatoms are normal, though kind of annoying to look at when you see your sand discolored and pebbled, I'm a big fan of crabs and there are a few that actually eat them. For all intensive purposes, though, there are snails that do a better job with it without compromising the potential for corals. I was lucky- for my 40g I had cerith and nasarius hitchhikers in my rock along with lots of bristle worms and other worms and inverts that took care of it for me- my 10g just had another diatom bloom, I'm waiting on my cleaner snails to get here. I am pretty new to salt, my puffer was my introduction, and, well, he started out as fresh, lol, and I've been a freshwater keeper, so I'm not 100% on this one as far as it being or causing problems, I'm kinda going through the same thing right now...