brown sand

Question
i have a 30 gallon tank with 4 fish and 2 crab and 2 shrimp,and i keep on having to rake the sand because it keeps going brown.Do you have any suggestions how to stop this

Answer
sounds like you have a cyno problem, best thing to do is get some phosphate absorbing media in your filter and do a total tank blackout for 24 hours. also try syphoning off the top layer of your sand bed, this will remove the spores that are present at the surface.