plant leaves Turing brown from middle of leaf and curling in

I'm not sure what's going on here. They are in roots organic 707 soil in veg under a 1000 mh turned down to 750. This happened over just 3 days, and I haven't been feeding them anything, just phd water. They are also running on 1500 ppm co2. Out of all 4 years I have never had this happen

sure looks like the lamp did it............

^^ i agree