| Personally, I would not recommend any chemical to alleviate your problem. In my experience with unwanted algae is WATER CHANGES and sufficient light/water flow. Ive actually done 5% water changes every day for two weeks when I had a spike in P04, it demolished the problem (this is my experience). Sifting your sand on a daily basis will agitate the algae and it will not be able to form on your rocks and sand in an aggressive manner. I would recommend water changes though...although lighting could be an issue, unwanted algae likes dimming lights. | 
