i would also say nute burn. the tips of the leaves are yellow. i would probably just use plain ph balanced water(6.3 - 6.8 ) for the next couple waterings. it sucks but at least you can still get an ok crop out of it. probably going to hurt your yield. another thing i found after growing for a while is if you at any time burn your plants during flower, no matter how well you flush them, your probably going to get a chemical flavor especially in a vaporizer.
as far as water levels, i would only water enough so that you water every 2 days. should be pretty dry and light by the 2nd day. lower temps will also make you have to water less often. keep temps about 80 in the day. for dark i go 75 but a lot of people go lower than that. i just do it to prevent mold/mildew since they dont like high temps. more water will also increase mold/mildew chances.
good luck