Aslong as you keep the nitrates and nitrites down all will be fine, the biodigest will really help, and i mean alot.
I did another roughly 30% water change. The nitrite and nitrate levels are better now.
The opae ula seem more active and visible since the heater was introduced, which is good, though it only seems to heat the aquarium up by 2-3 degrees. I am also now getting heavy condensation on the cover glass, so might link the heater to the timer I use for the lights to stop too much of the water evaporating while I am away from the tank.
The slime algae has also formed a thick green film on the surface of the water. Should I remove this?