The cause of the problem was that I was on vacation and the auto feeders were over feeding for a month

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thanks. my lights are 14000K and fairly new bulbs so i dont think thats it.

im gonna be trying to run 2 x 250 watt lights instead of the 3 i usually run, to see if there is any change on that section of the tank

Do you have reactors on your tank?

No reactors

I have been through two outbreaks. Never cleaned or treated. It goes away on it's own after a couple weeks. The best thing is flow. From what I read, you are doing all the right things, even more than I have. It's a bacteria outbreak that has to run it's course. Whatever nutrient it feeds on it seems to use up or perhaps another bacteria overruns it. I wish we could test for what "feeds" the various outbreaks. I am not a clean tank freak, I like a little and have various algae on the back glass and rock. A stable healthy tanks fights off a "cold". My theory for what it's worth.

Once this stuff starts dying, will it release everything it absorbed back into the water?

I doubt it, not with phos at 0 and proper sump and skimming. The other suggestion would be to NOT stir up your sandbed to any depth.

Reduce your feedings, manually remove it, reduce your photo period, keep powerheads on full and, be patient. I had an issue for about a year and I did all of the above and it slowly went away. As others have posted, chemicals are a short term solution. Reducing your bioload until it is gone will also help. I ended up getting rid of a few fish. If you take a quick approach, it will most likely come back. If you don't manually remove it, it can die off and affect your tank. I don't remember exactly what that does, but I wouldn't risk it.

It is a long, slow process. Good luck with staying patient. :) I know it got the better of me sometimes.

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