Help fast

Im in need of advice ive got six plants. They have been in veg for two month and are strong and bushy about 18 inches tall. The problem is this past week the large lower fan leaves started turning yellow then brown and crispy on the edges im using half nutes two time a week 10/7/7. Now some of the top leaves are getting brown and crispy on the edges and some have brown spots. I wanted to sex them this week and go into flower but now i want to get them healthy again first. I know pics will help so i will try to get some pics up tomorrow. But any advice today would help. Can it be a mag defencancy? Some of the leaves have got some brown crispy edges over night.
Peace

Come on people any help out there?

Flush out the soil with just water and try using no nutes for a little bit and see if the problem stops, it almost sounds like nute burn. Also what is the ph of the water you are using?

like keiah said flush asap run with no nutes for a week or so and see if they come out of it. make sure your ph is correct in the water you are watering with. but on some where i think its weedfarmer.com they have a problem chart helped me GL

how long have you been feeding with half strengths with?

at two months/approx 60 days if you are growing in soil there is not going to be much left in the way of nutrient in the soil.

If you have been feeding with half strength for a while and this problem has only just surfaced it could well be the opposite and that your under feeding them possibly a ph problem too.

Dont flush yet because that could make the problem worse, before you do a bit more information such as.

how long feeding nutes, what medium, what is the ph of the feed if you are even measuring it at all.

Heat of the grow room,

margins going yellow and then crispy could mean more than one thing