live rock turn BLACK

Question
Hello,
I read the FAQ about live rock problem and I have almost the same problem, but my is worst. I have the live rock for almost a month, the green algae turn into WHITE then now it turn into BLACK and some of the rock turn into DARK YELLOW or ORANGE. My tank(20 Gallons) is a new setup tank with pH 8.2, SG 1.021-1.022, Temperature 78(F)-82(F), etc..., using a 15 Watts Zoo Med Coral Ocean Sun 10,000K Fluorescent, I'm also use calcium, iodine, Strontium & Molybdenum to help the algae. Is the light too strong or too weak? Because its tallest part see to turn black first, HOW OR WHAT CAN I DO TO MAKE IT TURN BACK TO GREEN COLOR? AND DO THE BLACK ALGAE CAUSE ANY PROBLEM TO MY TANK LIKE TOXIC ETC...?
THANK YOU SO MUCH


Answer
Hi there, I am personally not familiar with black algae. Whenever I get algae of any kind the first thing I do is check the parameters as algae feeds off excess nutrients so I test my water and check if it had anything to do with that. Second thing is to check there is no natural light on the tank and that the tank lights are on no more than 6-8 hours a day (I usually drop it to 6 if I am having an algae problem) Hope this helps some, sorry I am not very familiar with the kind of algae.