I had a really bad red slime problem about 8 months ago. It was so bad that it made me want to give up. I agree with mr x, you don't want to add anything that might kill the beneficial bacteria. Everyone told me keep up with water changes and it should go away but the solution itself is not just water changes, if you do not find the source you will never win. Personally I did three things, and it completely won the battle. I am not sure which one it was or if it was the combination. I did them all the same week and in two weeks time it was gone.
1. My bulbs were old so I replaced them.
2. I added two power heads both with circulation towards the sand. Red slime is lighter than the sand and will float off if it is getting hit by a direct flow.
3. I added a uv
Also you said Los Angeles! What city? I've been to about every lfs
store from thousand oaks to fountain valley