leaves turning brown/ curling on new & old growth

hi folks help needed please !!!

my plants are turning brown on leaf tips & edges, on mainly older leaves & on some new leafs.
i dont have a ph tester at the minute im ordering one in next few days. however im not sure it is the ph.
i have cheese plants on 2nd week of veg.in coco soil, there are 16 plants under 2 x 600 watt dual spectrum bulbs with a 250watt between them(not switched on as yet), tent size 2 metre high x 1.2 metre depth x 2.40 length.

fed on water not ph tested.& 1/4 strength nutes ( hesi coco nutes ) every 3 days.
the nutes are supposed to be ph balanced or something so dont need to ph test them.

i noticed a slight spider mite problem on a few of the plants i have used a smoke fogger for the tent (plants removed whilst fogged) and have treated the plants with spider mite control foliar feeding.

the mites have pretty much gone now only a few eggs left.

need help please as need to sort the problem quick.

thanks for any help in advance.

stay on top of those mites, keeps spraying even when you think they are gone and you should be okay. I like to use azamax, spinosad and bt combo for mites. after getting your ph dialed and mites killed you should recover

thanks for reply, im not sure its to do with the ph though. does the plant suffer afterwards from the mites or recover ok ? the leaf tips seem to be dying off working up to the new growth. i intended to keep spraying the plants with the spider mite control after they have gone just as a precaution.

^I'm guessing it's PH, as well. Those things are starving, and unable to access whatever nutes are in the medium.

ok cheers, just been researching on the ph. gonna buy a ph tester. test my tap water then add nutes ph them and adjust accordingly & see what happens. cheers for the help.