Is this powdery mildew on my plant and is this run off PPM a good number

Man Chris I’m not even sure this is the first time I’ve used it the plants were looking good so I didn’t bother with it but I’m in 3 gallon pots with FFOF they are Autos from Royal Seeds I’ve only been watering every three days and they were looking fine so how do I check the ppm meter so what should I be at