Cultiwool Rockwool 6x6x6 Block w Optidrain (48 pieces per case) ETOH REV Filter Size Standard System Ratio PE Grow Bags Filter Size Standard System Ratio 1:1 Nominal Salt Rejection % 97% Permeate Flow GPD 1000 Permeate Flow GPH 42 Min Feed Flow GPM 1 and starter sheets is by far the best on the market with superb air to water ratio and a fibre structure that holds water longer and has less resistance for the roots to grow in The quality of their newest Rockwool cubes Cultiwool Blocks have an optimum air water ratio for healthy root growth and allow for great continued rooting thanks to the extremely even distribution of water and EC