Sand starting to turn brown

[marcingo]

Basically my reef has been going for just over 6 months now. In the beggining I used to have diatoms on my sand until I got a yellow cheek sand sifting goby. Then everything was great my sand was white. I had to sell him 2 days ago since I have to downsize my and he wouldnt be comfortable in the smaller tank. Anyway in two days my sand is now getting brown again. Is there any way for me to get rid of the browning. I know I can stir it (prefer not to) or I can lower nutrients in the systems(however the system is mostly softies and they flourish in the nutrient full system) is there any other way to do it? Any type of small fish that would be ok in a 20 inch cube that could do it for me?

Thanks for the advice.