Folks also consistently underestimate the significance of seeing their chaeto stop growing. It's fantastic at grabbing and holding nutrients, so if it stops growing that means your whole tank is most probably nutrient limited.
Very frequently so-called beginner corals go on to become pests since they are (generally speaking) faster growing, less susceptible to tank stresses and often more aggressive than "ordinary corals".
Bacteria vs algae is the magic scenario we hope for when we carbon dose our tanks – that bacteria will "automagically" make the algae go away. We see here that in some cases it does work out. But as we see next, a "balanced system" promotes all three lifeforms.