I am no expert but I have a 29gallon tank that I keep a reef in currently (will upgrade in 3 months) and the use of a combination of blue leg hermits (careful expect snail losses), scarlet, nassarius snails, & astrea snails I have a perfectly white/tan top level on my sand bed (live sand).
When I first started however the inevitable diatom bloom covered it, and the bottom layers continue to gather vibrant purples and greens over time (which i hear is good)... however that top layer is pretty sweet
for your info I use HOWEVER this dosn't mean that a algae eating fish wouldn't work just as well:
5 blue legs
10 astrea (for glass)
9-12 nassarius (lost a few due to crab related assassination)
5 scarlet
I have never had a loss due to starvation that I have seen but this is in a year old tank with 50 lbs of LR and 20 lbs of LS for algae growth. So ajust based on how much surface area you have in your tank.
I hope my modest opinion helps a little.