hey there mate can you post a picture...

how old are the plants and at what stage are they in... 3rd week veg. 6th week flower etc.

your tap water ph source is stated but whats the ph after youve added your nute and additives but just before you give it to the plants??? it should be between 5.2-6.2 if your hydroponic and 5.8-6.8ph if your in soil. certain nutes will get locked out at ph values higher or lower than those stated.

its normal for a plant in the very later part of flowering to loose leaves.

what is the ppm-ec of your nute solution by the way...

sounds like to little rather than too much...