Growth in tank
Appologize in advance for the noob question but im having a rough day haha. My tank parameters are fine 0ppm ammonia, nitrate, nitrite, salinity is within normal recomended range, etc. I have a protien skimmer. The tank has been very healthy along with all of the creatures within it, i have yellow polyps, tangs, and a clown fish, inverts, feather duster. I have been regularly getting a thick lining of a very dark almost brown / black coating on the bottem of my sand bed. I am not sure what it is, but it doesnt look the best, so each time i disturb it and take it out. When it is disturbed (broken up) it gets stringy and someone take the form of broken up sea weed. Does anyone have a clue what it is ? Some of it sinks below the sandbed, some is filtered out, the tank is fine for a few days then after a week or so the dreaded stuff comes back covering my sandbed again. Any ideas ?