I just did a 5th wc last night and I do 5th weekly...but by the next day all this brown is on top of my sand by the next day and progressively gets worse...I have both my circ pumps pointed to the 2 spots it is mostly but still builds up...
Ammonia 0 nitrites 0 nitrates between 5-10
Phosphate .2 calcium 440 alk 11 magnesium 1400 ph 8 salinity 1.026
My tank is about a year and 4 months
My cuc is various snails serpent star and red and blue leg hermits and a hh urchin
Your phosphates are high if they are at .2 - ideally you want then under .03 but under .08 is ok too. That could be fueling some growth. To keep my sand clean I got a sand sifting star, and just recently swapped him for 2 conchs.
