The present invention relates to a microorganism water quality modifier, particularly to a microorganism type grass control composition used in aquaculture, wherein the microorganism type grass control composition comprises main raw materials, fillers and auxiliary materials, wherein the main raw materials comprise Bacillus subtilis, Baclicus lincheniformis, Lactobacillus plantarum, Lactobacillus acidophilus and other beneficial bacteria, the fillers comprise zeolite powder, sodium chloride, magnesium sulfate, calcium sulfate, calcium hydrogen phosphate, and sodium sulfate, and the auxiliary materials comprise pregelatinized starch, micro-powder silica gel, dextrin, a starch-lactose complex, glucose, magnesium stearate, and microcrystalline cellulose. According to the present invention, the Bacillus subtilis, the Baclicus lincheniformis, the Lactobacillus plantarum, the Lactobacillus acidophilus and other beneficial bacteria are directly pressed into the tablets with the diameter of 4-12 mm by using the tableting machine under the dry powder state, and during the use, the tablets can be directly sprinkled through manual or machinery manner so as to substantially reduce the labor intensity, and the tablets sink into the pool bottom portion heavy pollution zone so as to directly provide the effect and effectively improve the use effect.