clone and nute burn questions

Hey all fellow cannaseur and medical growers alike. Im currently on my first grow. 10 x 10 x 10 mixed strain 12 site ebb and flow. 5 og kush 5 critical 1 sweet Mandarin (autoflower but its bigger than the og and less bud sites 3 weeks into flower) and a white widow. 2 1000w mh/hps eye hortlux bulbs. room temps 75 day 66 night humidity 48%. I wanted to get some pretty solid strains and i know doing a mix strain hydro like this is a little harder than most but i wanted to see what my room would produce well and what i kinda wanted for personal and medical reasons. (the auto sweet Mandarin is my GF's and its growing better than all the other reg photos...figures huh.....smh) but my question is this...... So far for my first grow its all going well. i didnt skimp on any nutes i bought everything i needed and are following most instructions in Gorge Cervantes book for reference.... i just follow GH expert recirculating label strength and added some cal mag. i have a nutradip tri meter i use to check my ph ppm and temps and so far we have tried to go over a little with just the micro/gro/bloom (whatever phase were in) by a few ml every time we top off with fresh water keeping a 1400ppm consistency. 3 weeks into flowering i experienced a little nute burn on one of the og kush and critical. im currently on my last week of "early bloom" and did a res change (every 8 days)got her settled at 1250ppm to see how they reacted. just some yellowing on tips and brown tips, some on mid of the plant and a few older bottom leaves. SO...my theory behind giving them more than suggested is to see how hardy a strain is in my conditions. so out of all 12 there were 2 plants of diff lineage got the burn. would it be safe to say that these two were the weaker out of the 12? so next grow... i get my e z cloner and i want to take clones i would try to keep the ppm at 1400-1500 and whatever grew the best pull clones from her? kinda like the strongest survive and reproduce kinda deal? im just trying to push my o.g. kush to the limit and get the strain maxed out before i start working on maximizing a sweet deep grapefruit or maybe even some GSC now that they are available to order. Thanks to any and all that chime in. sorry for wall of text....crankush is around in my area and causes rambling

*I labeled this for a feed time question but i ment to type clone and nute burn suggestions..