Brown spots (first timer)

You either have a ph issue in your soil or your getting a little lockout going on. You still have a month or more of flower so I would get a ph tds reader if you dont have one, check your runoff ph and ec levels to see where your at. If ec reads high, you will need to flush with the water ph where you want your soil at when your done your flush. If your ec was high and you had to flush the plant then re feed at half the rate you were feeding. Hope this helps. Cheers

I wouldn't worry this late in flower, they'll typically start changing on you around this point. I know growers who don't use calmag at all during flower. Cheers,