Red Slime Algae/need help

How does one get rid of red slime algae? Water parameters are 0 for ammo, nitrites, nitrates, phosphates, 78-79 deg...yet I have small patches of red algae in the tank, both on the LR and on the sand. Did I do something wrong?
I change 2 gal of my 20g almost every day, and 6 gal once a week, tank started July 20th, one ocellaris, one firefish, several assorted inverts including one cleaner shrimp. Diatoms not that visible in the morning, but seem to grow much more apparent at the end of the daily light cycle. (8 hours 48w T5ho)
Any advice appreciated

I was just doing a little reading on red slime algae.
A couple of things I will try, tell me if you think this is way out of bounds.
1. about.com had an article that said activated carbon can actually contribute phosphates to the tank. ( I change filters every four days or so) I have removed the carbon filter from the skimmer/filter combo, and replaced it with a filter pad only.
2. less feeding. I usually feed a small amount of flakes early in the day, and a small amount of mysis shrimp in the evening. I will cut this to alternating each type once a day.
I don't think the lighting is really that high, so I will leave it for now.

thoughts?