How do you know you have enough flow? Red slime is a low flow algae and simply blows away with too much flow.
Any algae requires light, so of course it will only grow where it can get light.
Algae problems come down to two things: nutrients in and nutrients out. You do not have enough nutrient export for the nutrient input to your tank. Nutrients input comes from two main sources: the water itself if you are not using RO
water for topoff and to make saltwater and from food. If you are using RO
water for both topoff and making saltwater then it is the food. This means you are either feeding two much or feeding low quality foods.
Nutrient export is done mainly with water changes. What is your water change schedule? It can also be done with a refugium where the macroalgae uses the same nutrients that bad algae will use, therefore starving the bad algae. This method requires you to physically remove the macroalgae as it grows, otherwise the macroalgae simply locks up nutrients but doesn't actually remove them from the system.
Live rock itself can remove nitrate via denitrification.
Most likely if you re-examine your system you should be able to find what is causing the imbalance.