Some areas have soft water others have hard water,by ajusting the ph of the water you can get it at the best quility for the plants.I always feed my water at 5'5/6.0 i find i have alot less problems with the plants yellowing through notrogean the guys from greenhouse in all there dvds never have there ph above 5,5 to 5.8 and this something in these dvds that everyone can try since switching to this i have had no problems at all and bummper crops bro.it's all to do with how good the water is treated at the water plant.also flushing on a weekly basis a little extra work but i swear since following the words of franco and arjon my crops have trippled.take a reading of the water that first comes out of your pot to check if the ph has highered or lowered.we can go on for ever about this subbject bro but i hope this helped.Also always make sure that you add your nutrients while water is in the bucket then take your ph reading i leave a shower hose running to mix them while i add the nutrients.belive me bro its all a load of information that the simple grower of a few plants don't realy need to get into.Has long has you feed the plants the right ammount of nutrients don't have a too higher ph keep your light has close has possible i'm talking inces off the tops.Make sure that the grow room has a good air intake and a good air exaust plenty of co2 you will be fine.Too be honest growing has been made out to be alot harder than it is.