Coralline Algae Dying?!

i am having the same problem, perhaps someone could give me some suggestions too...i'm runnin 55 gal wit 70 lbs lr and have one large rock that i bought 5 months ago and it is covered wit purple algae sittin on top of my aquascape. the algae spreads to all the other rocks, sand, and glass, but never seems to actually get into rock. i cut my lighting from 10 hrs to 8 hrs due to excessive algae on glass (need more snails) but that caused massive die off so today i stepped up to 9 hrs. it will spread quickly but later die off on everything but the 1 piece i mentioned at top. all my water tests come up good, doin my changes, slightly low salt concentration, and 4-48" t12 bulbs (1 is 10oook, 1 is blue actinic, 2x4100k), poor water circulation (marineland 400). offer cheap suggestions cuz goin through divorce

 

make sure your calcium is not too high as well