Going without a clean up crew is difficult but not impossible with excellent filtration (high quality skimmer) and good water movement. Keeping your no3
at 0 ppm
is key to an algae free tank. I wouldn't worry about the Tusk and clowns but the Firefish is not aggressive enough to house with the Tusk.
As Lindsay mentioned a fairy wrasse would be a better mix with the current fish you are considering.
What current stock to you have now? Are you providing an nh3
source to the tank while you are waiting out the ich to keep the bacteria going?