Yellowing and Dying leafs few weeks old

I am starting to stress a lil. My plants have started to yellow or I should say there green is light in color. I have looked into many solutions but I am not "aware" enough as to what is what. I have some fault as to knowingly useing methods I cant avoid right now because of the 2 grand I dropped to get this running. 1st I am using tap water at the moment and I know from life that it is hard. I will get some strips to test it till I get my ppm/ph stick. The leafs on a few of my plants have turned brown and look to be dead. The yellow pigment seems to picking up as well. They seem to be slow but am looking for opinion on that. Other than that they are beautiful and seem look healthy. I have them in 6" rockwool running 24 hr light. Water 3 times a day and measure good or bad by the weight of rockwool cube. I dont feel they are over/under watered. I aslo am curiouse about there maroon stems ALL of them. Any how I will come up with more so we will see. Oh and NO NUTES have been used but I am wondering if maybe I should. I am just skeptical because of there delicate stage ? I have a plan but would love to hear from EXPERIENCE of your mistakes than make my own. Thanks ladies and germs.

bump bump bump
BIG help guys

get some nutes in there maybe half strength to start off with

Started quarter strength to unlock them. I believe from the red stems that they are missing n,or p, or one of the above. We will see.Here is a good spot to check health of plant.http://www.weedfarmer.com/cannabis/tables_guide.php

You might want to start off with only 1/4 strength, They are still pretty small. Hard to say if you can't check the ph. That could be a big part of your problem.

Probably overwatering - With plants that young, and 6" rockwool cubes I only water one or two times per week.

Thank u both. Yeah I'm well aware of the PH prob. I am looking to get strips for a short while till I can get my pen. I mixed a milk jug 1 us gallon with a diluted nutes. I am using B.C Boost,B.C Grow,Thrive Alive B-1, MagiCal,and Sugar Daddy. I shut off my watering timer and am going to deal with these waterings personally till I see change. I also put another small fan in my room and turned the AC up a lil so instean of 79-83 its now pretty consistent with 75-77.I feel this is narrowed down to Deficiency,Heat,or the hard waters PH level.