Frustrating Algae Problem.

Okay, I'm relying on the collective experience of this forum to help me with an algae problem I've been dealing with for the past month. It started small and is slowly taking over my entire tank.

Some background info, I started my tank November of 2015 with about 100lbs of live rock from an aquarium that was established for about 10 years. I planned on running a super low nutrient tank and had been successful. Everything was running flawlessly and the water was pristine. I had coralline algae growing everywhere, the live rock was nearly completely covered in a matter of months. I couldn't have been happier. That was until about a month ago. I noticed at the top of my tank a dark brown, almost maroon algae growing on the live rock directly under my radion lights. At first I thought it was more coralline that hadn't purpled up yet and didn't worry much.it didn't change color, and kept spreading. I became concerned so I reduced the intensity of the light and shortened the photoperiod, to no avail. I'm currently down to a 10 hour photoperiod which begins at 10% intensity in the morning and peaks at 60% before tailing off in the evening. This has not slowed the progression of the algae (or what I believe to be algae)

Ive checked my water parameters throughout the process and my nitrates, nitrites and ammonia have been 0 every single time.

During my searches I've come across pictures of diatom blooms which look similar to the algae on my sand. Checking the causes of diatom blooms I noticed high silicate levels could be a cause. I bought a silicate test kit and, in true fashion, 0 silicates. I can't for the life of me figure out a) what this mystery algae is and b) what is feeding it.

Any help would be greatly appreciated. I've attached some pictures for reference.




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Do not know of you are still having a problem with this or not. I once had the same thing take over my tank. Never did figure out what it was. However, the only way I got rid of it was by lowering the intensity of lights and by only having lights on Every other day! On the days where my lights were off I also did not feed my fish. In about 2 weeks it was all gone. This happened a couple times and this is how I took care of it. Now that my tank is 2 years old I have not had it happen again in about 6 months.