The powerhead got rid of the green slime by altering the environment, not reducing the available nutrients. So the red slime is just taking advantage of the (still) elevated nutrient levels.
Feed less. Skim more. Siphon to physically remove the slime (this removes some of the nutirents bound up in the slime as well).
I siphon slime with a half-inch rigid plastic tube about the depth of my tank, connected to 1/2" ID flexible plastic hose. Get the end of the tube close to the slime, and it should suck it up without removing much sand.
Also, check your alk more often. Alk will sometimes drop due to the nutrients that can fuel slime algae. And when alk drops, many skimmers don't work as well.