sorry i've maybe not explained properly, i only let my water sit so i can heat and aeriate it, i only add nutes when i need to, ie i mix up two litres of water with nutes at a time as that is what my watering can thing takes. I've got about 80 litres of water in my tank, and i take out two litres and then add nutes, reason i was asking if i should make ph of water in my tank higher is because the ph up and down that i got states 2.5ml per 90 litres, and not sure how to work it out for such a small amount of water. so if i was adding the ph up to my 2litre water can with nutes, not sure how much ph up i would add. sorry if i'm being a pain!!