Hello there. I have a new 300 gallon tank. It has two 250 watt metal hailde lights on it (10 HOURS per day). I have a sand bed with real sand (not agronite). Only in one spot in the tank there is a build up of a grey/purple algae. I mix the sand with a stick every day to try and break up the algae. I'm guessing it is there due to a low water flow area. Everywhere else in the tank the sand remains pure white. I'm probably going to purchase a second pump for that side of the tank and generate more water flow but wondered if anyone had this problem or knew what kind of algae it was. I have several blue legged hermits but have not seen them eat it. Is there anything I could use to eat the algae? Thanks for all of your help. Brian