Occasionally get this problem

My method is hydroponics with Botanicare line nutrients.

Climate is always between 72-78 degrees.

PPM @ 450 and ph @ 5.9

Water is R.O. and supplemented with cal-mag.

C02 at 1300 ppm and humidity is at 60%.

They're under 1000 watt hps lights.

These girls are in week 3 and I get this happening very rarely. And I don't change anything up. But what the hell is it?

I've searched and searched and haven't really found the solution. Any guesses?

Thanks

Cal-Mag. IMO

Damn... I was thinking the same too.
Appreciate the help. Thanks.