you were very vague on ph not below 5 not above 6.5.so what is it exactly?perfect uptake on nutes is around 6.2.so if your down around say 5.2 or so this can cause nutes uptake to slow which can cause certain nutes not to uptake like nitrogen which plants need a good bit of at a young age. im guessing you don't have a meter and are working off of the drops? another thing is ph swing it's not good to have your ph jumping so much 5.0 to 6.5 it's not a what ever game you need to be on top of it.

first thing i do if i ever have a problem is ck the small things first.alot of times people overthink and ck everything but the easy stuff. ph and temps should be on the list of first things to ck.as both of these things can cause nute lock out. now when i say temps i mean room temp and root zone temps. you need to get a meter,ck these things first then if everything is in line then go to the next in line i.e light is ofcorse a main factor lol and nutes and so on.