If you are using clay pellets (hydrton), then it is from the dust that's not completely rinsed off.
genuine Reviewed by genuine on . 2 Dumb Questions I should know I have a 5 gallon bucket with an air pump running 24 hs with fow farm grow big and big bloom. There seems to a red preciptate that collects at the bottoom ( see pic). Also is there a point in bubbling water to purify water. I can't afford R/O or distilled in the quantity needed Rating: 5