Yep, sounds like diatoms to me. Often caused by insufficient light or a nutrient imbalance. They will go away on thier own over time but if you want to speed up the process, higher light intensity (more lights), keeping water quality excellent & adding co2 will get them to go away faster. If you don't already have them Otocinclus or Bristlenoses are good for eatting diatoms. It's hard to say if either of those are suitable for your tank though without knowing what other fish are in the tank. Some snails are good for getting rid of diatoms to. I believe Nerites are one of the better ones.
I have decent lighting and i have just bought a sucking loach. What are diatoms?
More than 10 years
Sucking Loaches don't eat Diatoms as far as I am aware. They also get too large for your tank & as they get older they get vicious. IMO it would be best for you & your fish if you were to return your sucking loach/Chinese Algae Eater.
What we percieve as bright light is not necessarily the case. When it comes to aquariums you can need considerably more light than you think. Can you tell us what kind of fixture you have (Flourescent, PC, CFL), how many tubes/bulbs there are & how many watts the tubes/bulbs are? The tube information should be written on the tubes/bulbs. If it's bulbs you will have to pull one of them out as the info is probably written on the threads/bayonet.