Heat stress or nute burn/deficiency?

hey guys i have 1 g13 haze in a 20l airpot low stress trained under a 600w hps.It has been in veg for 5 weeks and im gonna start flowering next week.i started feeding her last week due to two two of the bigest fan leaves yellowing around the edges.I have fed her twice in this week both times feeding half a ml of sensi a+b per litre.my temps sometimes get up around 88 max but generally stay around 80.
the tips of the new growth have started to yellow since i started feeding nutrients.do you think i should go back to just plain water? ny advice would be welcome!!!!

im itrested wat ppl say..so ill stick around for anwsers

Yellowing on the leaves looks like a bit too much N too me and this could be just The strain u got going but looks under watered too me the leaves look droopy

definatly not underwatered! overwatered if anything but i dont think so.i water every 3 days and give her 3-4 litres.

Wtaer with the weight. Whats your ph? It looks like it could be a mg def. Not to bad though. I think a N def would start at the bottom and work its way up but i could be wrong

i always water when the pot gets light and my ph is between 6 and 6.5. i think you could be right with the mg deficiency.