I battled HA for a few months along with Cyano bacteria when i set up my 12 gallon fluval, and all i did was:
1.) remove any natural lighting (ie. sunlight next to windows)
2.) reduced my LED tank lighting by 2 hours.
3.) tossed in an emerald crab* (I pluck some of the taller stuff too right before i do a water change)
4.) weekly water changes with RO/DI ultraviolet polished (Type 1) water.
I'm currently working on my dad's 300G tank as his was overrun by HA and so far just using steps 1 and 2 we've had a significant difference.
*one thing to note is that HA in large amounts is considered toxic to your inverts, at least that's what I have researched, so hitting it with large amounts of "borrowed inverts" may help as well fyi.
