I have diatoms in my 75G a year and a half after set up. I tried Ottos (bougth six) but they were too fragile. I now have a 150G set up for 6 months and have major diatoms.
Both tanks have African Cichlids now, so Ottos are out of the question. I heard Bristle Nose are, all around, the best for diatoms and green algea. Afte a year search, I found them in the new Big Als that just opened up down the street. I bougth a 5 inch one and put him in the 150G. A day later I couldn't find him, so I was worried the cichlids had eatened him. Then I noticed the obvious, the diatoms were gone; I mean completely gone! Every tank corner, rock, and drift wood. I spotted him this morning under a rock and his fins look okay. So this may turn out to be the perfect solution.