Block Clean keeps your growing media clean and free from unwanted biomass throughout your plants cycle. Biomass can become a breeding ground for disease pathogens and should be treated as soon as it is seen. Block Clean Spray can be used on any growing media that attracts biomass (green sludge) and there is no need to remove your plants from the growing media before using this product, just shake well and point to the infected areas and spray. If the biomass is quite severe it may take a couple of treatments with Block Clean to remove it all. Block Clean is not recommended to use on seedlings or cuttings.