I'm way behind on what's been going on in your tank for awhile now but Downoi rarely melts once it's acclimated in a tank unless some major water chemistry changes in the tank.
It sounds like you have new lighting which can throw a tank way off balance! I did that with my 220g awhile back. To get all the algae under control back lighting down to 5 hours or do 3 on, 2 hours off, and 3 on again. Spot treat what needs it and get those nitrate and phosphate readings. Even more importantly get a kh and gh reading. Curling leaves can mean a calcium deficiency or even too much potassium or magnesium.
Staghorn also likes low CO2 amounts in the water so if you can increase CO2 that can often help along with spot treating.