2 Month in veg, Piece leaf missing .. no sign of insects

So i`m in my second grow, i`v OG kush in her 8 week (just flipped to 12/12)
growing in coco+per / 250w dualspectrum hps / just transplanted from 2.5g to 7g pot
using AN SENSI grow+bloom (a+b), temp`s are 72F-82F.

recently i noticed that some of the leaves looks like they been eaten by something. i triple
checked for insect and didn`t found any thing, in addition the tips of the some leaves starting
to burn. i have no idea why its happening but maybe its from the same reason =/
I just done with flushing between the veg and flower period and was feeding with only
ph`d water for the last 5 days. before that my EC was around 1.3-1.5. beside that she`s
looking great, strong and with dark beautiful green.

any input will help a lot!
thanks.

Did it happen after you flushed? And did you flush with just plain water?

That was your problem-feeding them just water! I missed that part, lol.

In coco/perlite if your watering till run-off each day you shouldn't have to flush until right before harvest.

If you have to flush for an emergency, ALWAYS use 1/4 strength feed, straight water stresses them out and they will show all kinds of deficiencies almost immediately.

I agree. But I don't see a Cal/Mag listed......add one in coco! How about you Bill?

Thanks for helping guys, it does make sense not to flush coco for long time =]
so what now?start with a regular flowering feed? about 1.2 EC and add more nuts when times pass?

thanks!