Firefish dead now.
10mg per gallon things were going well. Yesterday the briopsis started going downhill quickly. Not sure like I said of the massive amount of die off changed water parameters to quickly. In process in testing nitrates and phosphates. Honestly this was a battle with briopsis That I was was losing. It's still dying and if I lose a few things in the process, it's better than tearing my tank down. I do not regret doing this but if massive amounts of dying algae release enough phosphate etc then it's worth either running a skimmer or to pull as much out as you can. I took the advice not to pull it because it wasn't as effective. In hindsight I would have removed as much as possible first to minimize what was being brought back into the water column as it died.
Again I am still 100% doing this treatment. And am still moving forward. Nothing else was killing this stuff.
Side note I did start skimming again and it's going CRAZY emptied three cups already and waiting for my ro for a large water change