New growth with yellowing tips & a twist ?

Marse · Jul 3, 2020

Most of the tops are showing signs like this one! Leaves doing a twist & top leave tips turning bright yellow, what am I doing wrong?

Light is Mars Hydro Ts600, 20" distance.
Temp is between 23c (73.4f) - 29c (84.2f). Have been in a heat wave for around a week now, with another week of potential 40c (104f) temps outdoors.
RH is between 40% - %50
Ph tested with meter to 6.5, give or take a few. (soil grow)
Rotating between water and nutrients. (water/nutes/water/nutes)
Feed as per needed by weighing the pot, usually twice a week.
Water PPM from tap (no nutes) - 55
Using Rootfarm Nutrients ;

Part 1 - N(4%), Soluble Potash(1%), Cal(5.5%)
Part 2 - N(2%), Soluble Potash(7%), Phosphate(3%), , Mag(1.7%), Sulfur(2.3%)