Hi everyone, I started my tank with DSM about five weeks, and I mentioned that my white sand turn to brown. When I take a look closer, I saw this Is that algae? If it is, how do I deal with that. I use light for 4hrs and 6hrs with 2hrs rest between. I'm using flourish excel mixed with water to spray plants everyday, since I heard that excel can prevent algae. It just appears this week after I added more hemianthus callitrichoides.