Slow Growing Cyano

Hey all,
Would a TDS reading of 3 ppm and 0 phosphate for my RO water affect my cyano problem? I had a very serious case of cyano and I've been battleing with it for months. I've managed to reduce it significantly but have not gotten rid of it 100%. It's not growing way out of control. Its growing very very slowly but growing none the less. It's driving me nuts and I cant figure out how to get rid of it completely. My corals are flourishing and doing very well so I assume its not the water quality. To give you some background:
24g nano cube with (1) k2 powerhead and (1) knano powerhead.
Things that I've done to fight cyano:
1. Increased flow by replacing a k1 powerhead with a k2
2. Reduced feeding
3. Vacuum out cyano with every water change
4. Make sure magnesium, alkalinity, calcium, and everything else is at the proper levels.
5. 10 gallon water changes every week.
6. Replaced chemi-pure and purigen with new filtering material
7. Test RO water with TDS and for phosphates
8. Lights (metal halides) are only on for 6.5 hours a day
Things I'm Considering:
1. Replace the metal halide bulb (only 5 months old).
2. Add a protein skimmer
At this point I'm starting to wonder if this is even cyano. My LFS suggested that my clean up crew maybe inadequate. I have about 15 scarlet hermits, 7 nass snails and 5 ceriths. So I guess back to the original point. Do I need better RO water and if not what else can I do to fight the cyano?


If you had a big enough tank a Conch would eat it up. But then it would soon starve after eating up the cyano