Im lost. Signs of nute burn with 540 ppm

I'm growing some violator kush with DWC hydro. I keep getting burnt looking tips and rusty colored burnt looking edges. It looks like nute burn but I cant see them being burnt with low ppm. Is it lloking like this due to how low it is?

check everything ph, ppm, heat from light, it might not be nute burn

PH 5.7. Res temp of 70-73F. Room temp 77-80F. PPM 540. 600 watt MH's approx. 20" from tops. Air cooled reflectors pulling cool air from ac through

Sounds like you know exactly what you're seeing but trust a little meter better than you trust yourself.

Ask another meter for a second opinion?

You could just have really sensitive plants, my Afghan burns a lot easier than my AK48 does, some strains just don't eat as much, back off on the nutes and see if it helps, if not start looking for other problems.

i just had a problem like that 2 i couldent figure out why my babys looked sick everything seemed perfect BUT my ph pencil need 2 be recalberated (sorry my spelling sucks) so my ph was off even tho it read on, i took it 2 the hydro store and they reset it, within a day all my babys bounced back, odgrop is right 2 some strains are sensitive i wont grow urkle any more because you got 2 baby the shit out of them

I had ppm of 240 at week 4 and I had nute burn. Go figure.

Are you growing in a commercial tent or home made setup?

i am goign threw this problem right now. are you using tep water? if so try using distilled. might be the weater.