could be a lot of things more information helps, could be nut burn, could be not enough water, could be to much water, whats your ph of your soil of your water. also not enough nutrients gives us some things to work with like what you feed it how long inbetween you feed it and your levels
i'm using the grow tent i us advanced nutrient micro 5-0-1 and grow 2-1-6 the stuff that come with the kit the ph is good i feed every 2 days and water everyday and mist 3 times a day hum has been low but have brought it up 2 26%
I have 2 of those PH meters, they are wildy inaccurate.
Nutes every 2nd day is too much.
Give them a good flush to clean out the medium and start nutes again but once a week only.
You have to build up the nutes slowly.