Purple algae growth and a feeding question

[newreefer_59]

Have a 150 gallon SPS/LPS and fish tank that has been running for 4 years or so. have had to rent out my house about 9 months ago and the tenant is caring for the tank, but I do visit every 3-4 weeks to check on things. The tenant does a 20 gallon water change every week, but aboit a month ago I started losing 90% of my SPS coral and some is now covered in this purpleish algae. Bleck! All the fish and LPS coral seems fine and tests are reasonable. On thing was the lady let the SG sink to about 1.02. We have since gradually brought it back to about 1.026. Any thoughts on how to get rid og this algae.

Also, I have been asking her to feed mysis/brine shrimp about the size of a dime for their daily meal - along ith Spectrum pellets. Is this too much feeding?

Thanks all.