Since they are slow growing, they don't have a huge effect in terms of ammonia and nitrate. The good thing however, is since it is actually an algae, some people believe that it will keep algae at bay since it will take up the nutrients other algae would need to grow. However, I have no scientific evidence to back it up. I would think it would uptake nutrients, but how much I don't know depends on conditions of the tank as well.
15 Gallon NPT
1g no tech bowl in the making