Guys please tell me what can give such a sediment?

If you keep your water cool, 62 to 68° this is where water holds the maximum amount of oxygen and this is where your plants will do their best, you can grow warmer with adding expensive crap to try to keep slime at bay but a chiller I found essential for football size buds,which is what you should end up with growing hydroponics, not dirt grow size or smaller bud. I also found DNF, Dutch nutrient formula was made just for hydroponics and no matter what most big growers tell you they use,they use DNF cheaper then the rest for hydro and it is tried and true. Cheers