brown leaf edges

"Help" can anyone help i have started with brown leaf tips on my young plants, first week in system 3 weeks old i am not sure if it is heat stress temps 25deg c or potassium def i am running flood and drain system.
I was using dutch master for the fist time a and b gold range with add .27 at 0.8 ec.
I have now gone back to vitalink max a and b at 0.8 ec to see if this will sort the problem had no problems with this before.

Running 250w cfl temps 25deg c light on
21deg c light off
humidity max 60%
min 45%

.8 ec is 400ppm should not be too high, I would try lowering th ec I believe brown tips is a sign of overfert. don't know if you have one but here's a conversion chart.

"update" now i using vatalink max everything is starting to look good again i think the dutch master must have something a little strong in it for small plants even if the ec is at the recommended level.
Its a funny old game ha ha