For coraline algae to grow fast you need to have your water within certain perameters. Calcium 400 to 500 ppm, carbonates 7 to 14 dKH, pH 7.8 to 8.3, magnesium 1300 to 1500 ppm, the presence of carbon dioxide (it is a plant after all), iodine, manganese, potassium, etc. etc...
Frequent water changes with the addition of magnesium, and a cacium/carbonate buffer works well.
The best way is to install a calcium reactor and get it tweeked properly.
Also, if you want deep rich color then don't use more than 2 or 3 watts per gallon of actinic blue and daylight lighting. You still get coraline algae with halide lighting, but it isn't as deep in color (closer to the top, the paler the color).