Filter out Phosphates, regardless what test is showing, your live rock and sand is a phosphate storage, you may read low in the water column but that doesn't mean actual phos are low, if you have algae that usually means you have phosphates.

Hey man, the red slime is probably a bacteria called cyano, and isn't in fact an algae. You can go to any local pet store and ask about it, they should have a powder that you dose the tank with (will cost about $10) and it should kill off the bacteria within 48 hours, unless it is really bad and it will take two times that long. I had the same problem and this cured it really well. The red stuff will die and turn brown and if you have snails they'll clean the dead stuff up. Hope this works for you, let me know.

And oh yeah, if you are using flake food, then the cyano is prolly a sign that you are over feeding.

This has worked for my system
 

You have a cyno bacteria which will take over your tank and may harm your corals. Your live rock and sand(?) are more than likely saturated with phosphates. You need to remove all of your live rock/sand and place them in a covered, heated tube for a period of 3-4 weeks (or more) with a small skimmer or water changes (every 2-3 days). This will allow your rock/sand to re-cure. Clean your rock first (toothbrush works great) and re-clean at each water change. Only place back into your main tank when water stays clean, rock smells and looks right. This sounds drastic but just adding chemicals is wrong! You have to find the source of the phosphates and eliminate them (overfeeding/overstocking). I have found adding a Phosphate Reactor to the system along with good Reverse Osmosis water will prevent further issues.

re
 

yeah, that would work too. But more likely than not you are simply over feeding. That's what happened to me.

Yes we have discovered that it was an over feeding problen. I have a few corals that like to be feed and have had recieved some bad info about a few other that don't need to be target feed. So now I am only target feeding a couple of my coral that close over the food right away and eat it all and not the rest. going to check phos levels again tonight and have ordered some Zeovit Coral Snow. Removed all the red algae ( was not slimy) peeled of in a fine sheet, small piece's that I could see and get to. As I have a 155 with about 80 lbs of sand and about 100 lbs of rock removing it all to clean and kure again is not really an option right now.

I have a whole house RO system (massive $$$) Water quality better then store bought. I think I will invest in a reactor. Got any sugestions on what to get?

Idea though is get a good overall flow, not blasting it all out of one or two nozzles.

I use Two Little Fishies PhosPhate Reactor 550 with their PhosBan Media on my 140 gallon with great success. They also have a smaller unit , PhosPhate Reactor 150.

I have 4 sprayer bar's run off a 1100 gph little giant pump and 4 1300 gph powerheads. All pushing in a different direction.

Do you run then from your sump or out of the main display tank?