I have snails for diatoms. I had a bunch of pond snails but Tango ate all but the big one. :/
The one big guy does a pretty solid job of it.
For my other tanks (as well as Tango's) I use Flourish Excel to try and keep the diatom problem down. It doesn't really do anything to them but it helps my plants stay healthy and they in turn take in more nutrients so the diatoms have less. Or at least that's what I read. It seems to have worked. The diatoms in most of my tanks turned into balls of fluff and fell right off the plants.
But if I forget the dose for more then a day those pesky diatoms come creeping right back up. With a force. LOL!