Morning daco, I ain't no expert by no means but if you have kept your PH, right like you say, I would try feeding them with about one quarter strength nutrients, A little tip burn is usually not a problem, but like in your situation I would want to find out the cause too.
. Maybe someone else will chime in ,in a minute or two.
Sounds to me like your plants are a little short on nutrients though. Good Luck with them Daco.