[reefgeezer]

A multi-pronged approach might be advisable.

1. Add clean-up crew to include Urchins
Some algae is always trying to pop up in healthy systems. You need things to keep it from getting out of hand.
2. Skim super wet and replace water with new ASW
This removes the most bad stuff possible. The additional new water helps the cause too.
3. Vodka and/or vinegar... it will work
4. Elbow grease... where possible remove the HA. You could remove any rocks that are possible to remove and scrub them with H2O2 also.
5. Run GFO & pay attention to when it is depleted

If you have HA, you have available nitrogen and phosphate regardless of whet your tests say. Don't add more. Quit adding stuff to "kill" the algae. Be patient.