Diatoms in a cold water aquarium. What to do?

[Chapin]

Hi ppl,
I have 2 10 gallons aquariums, one with 4 3" golsfish, 2 snails and a pleko. Im facing a diatom problem, i think it s from the light, i use to have the same problem with my other aquarium(plattys, guppys and an ottocinclus) and i bought an ottocinclu and the problem was solved.
For my cold water aquarium, i bought a pleko but the problem isn t solved, is there a special fish i could buy? Do ottocinclus live in cold water? Please help me out