Hey Draug, I saw your anubias post. Are the spots little holes at all? Holes are a light issue (too much). Have you tried gently rubbing them off with something like a damp cloth? If its algae, itll probably help to rub it off.
Anubias grows so slowly that its a prime target for algae to attack it, which is a shame. An occasional rub-off of it with a cloth will help it if so!