What is the make of test kit that you used? Also, don't use buffers to correct pH problems as this will raise the alkalinity. The Ph can actually fluctuate a little throughout the day and 7.8 is fine. Having an alkalinity that is too high can cause a lot of stress to corals.
Here is a run through of things to try. How big is your tank and give us a run down on your equipment
Red slime boils down to having too many nutrients in the tank. If you can control the nutrients you won't have much growth.
Adding more of a cleanup crew just adds more bioload that requires more food to maintain and can actually make the problem worse.
some suggestions
1). Increase the overall circulation in the tank. red slime doesn't like a lot of movement in the water.
2). Check the source of water you are using. Use RO/DI water or distilled for all of your make up water. If you are using RO/DI
change your membrane and cartridge regularly and inspect the water you are getting with a tds meter.
3). Do regular partial water changes and remove detritus as you see it.
4). Regularly clean, rinse or replace all mechanical filtration components. I find a weekly rinsing of all mechanical filters goes a long way.
5). Be careful to avoid over feeding.
6). Use a high quality activated carbon and change it regularly. So far I have used bulk reef supply's carbon and it is the best I have ever used.
7). Use Purigen and recharge it regularly
8). What skimmer are you using?
9. Consider using a good quality GFO and get a reactor. It will help lower the phosphates.
10). scrub down the affected areas with a tooth brush and siphon off all the detritus around it.
there are other things you can try of course but the main thing to remember is excessive nutrients are the problem. No nutrients no red slime.
