rock and sand help. Wish sand you could run a DSB (deep sand bed) this will help reduce the amount of nitrate being produced as an end product. In any fish tank, this will accumulate and will have to be removed. Some tanks stabalize better and dont have much ammonia to begin with, but with the addition of fish and organic waste, IE food, there will be nitrate through the roof in no time. Water changes remove this unwanted nutrient and will reduce the amount of overall algae growth.