I had a few outbreaks of GHA..first in my display then in my sump. A good batch of urchins, turbo snails and hermit crabs did a great job...especially since I initially overstocked it in the hopes to clear it out. HOWEVER, i really never eradicated my GHA until I put in a turf scrubber. I dont know if this was just coincidental timing or if the turf scrubber made it so that GHA 'decided' not to grow any where else...but I have had no problems since my turf scrubber has gone in my sump.