Why leaves curling up on the tips

Trying to figure out why in the last day my 2 autos in DWC why the edges are curling up pH water is 5.8 and temp is around 79 and is under the 180w aglex quantum board at 22inches. They are doing great at under 3 weeks old and this is first signs of any stress. I used 10ml of 3% peroxide to clean up the reservoir it is a 7 gallon container ... Could it be the peroxide? Ppm are 400 Dyno grow foliar pro and pro Tek