I had what I though was red cyno covering the sand and some rocks that I have had for awhile. After doing a couple small water changes (10%) two days apart I woke up this morning and the red mat on the sand changed to a green color and my skimmer is going crazy. When my lights came on the water has a pink tint to it and there are so many pieces of this green stuff that used to be red the day before floating around. Here is a pic of what is on the sand bed that was red and turned green overnight.