So bryopsis has a fan like structure, upon closer inspection is it strands of hair like algae? Or is it fan or comb like. Best option is to send a picture, preferably in whiter lighting. While your tests may show in range, it's because the algae itself has the excess. What this means is you are only testing for what is in your water column, not what has already been consumed. Removal of the algae by hand will remove what you can't test for. I hope that makes more sense. Get some airline tubing, and a rigid straw or acrylic tube to attach to the end. Start a siphon and suck the hair algae into the tube, then pinch the hair algae at its base and pull, it will suck right out into the tube.
Gha stands for green hair algae and gfo is granular ferric oxide. Putting gfo in any type of reactor will allow it to absorb phosphates out of the water column before algae can consume it.
After we identify what type of algae (I'm no expert BTW, just dealt with this on many occasion) you can proceed with treating. It will take time, usually takes me a few weeks to fully eradicate gha in any of the systems I've dealt with.
There are other options, like vibrant, which I have no experience with, but I can assure you that manual removal and an export of phosphate will help get rid of gha IF that's what you are dealing with.
