Diatoms are common in new tanks, but once the biological system has stabilized, one rarely sees it. There are fish that will eat diatoms--I hesitate to say this because adding "x" fish is never the solution to algae or snail "problems." But if you have space for properly providing what these fish need, and provided you like the fish as a fish, there are several that will eat diatoms and common green algae--but these will not touch any "problem" algae like black brush, etc.
Otocinclus; a shoaling fish so a group is needed. Bristlenose (Ancistrus sp.), best alone (males are territorial). Farlowella species (so-called Twig Catfish). The small Whiptail species like Rineloricaria parva are said to eat diatoms, I've had this fish over many years but I didn't have diatoms so no idea how good a job they do. I do know that the otos and Farlowella were incredible; one has to get them used to sinking algae/kelp-based disks so they will not starve when the algae is for all intents and purposes dealt with.
Snails will certainly eat diatoms. Don't know about shrimp as I've never had them.
Otos are safe with plants. The same cannot be said of Farlowella, they will chew holes in soft plants--they decimated my chain swords some years ago, but in the larger tank with the larger sword plants, not a problem.
