The information that I have gathered from this forum has been excellent and many thanks go to yourself and the other people that give such terrific advice. I am now dosing using the EI method, but I have a query about doing the 50% - 70% water changes. It's very easy for me to do WC's as I am set up for it with aging barrels and pumps etc. What I need advce on though is that my tapwater is approximately a p.H of 8.1 When is the best time for me to do WC's? If I do WC's after the lights and CO2 have been running there is a big p.H swing as the new water goes in and the p.H goes up then there may not be enough time before lights out for the CO2 to bring the p.H down.