What now? Macro algae question

[CSJIII]

I just havent had good results as of late and now whats the problem? I had some macro algae on a few of my rocks for a while and figured no big deal. It was nice and green and my emeralds were eating it. Now, in the past two days it all turned grey and have no idea whats going on. I have been doing 10% water changes twice a week to get my cal levels down from 550. My alk is 9.6 and Mg is 1380. I have had some cheato running as well. I just tested nitrates and they are 20ppm with Po4 at 0.01. Here are some pictures. Can anyone tell me what happened? Should I do something?

 

[ritter6788]

Maybe wilting and dying since you keep your tank clean.