Brown spot during flower

Looks like phosphorus but without any other info you can’t assume that. Really should have a diary if you’re asking questions

Phosphorus deficiancy... Check your ph and had a balance solution with a higher phosphorus %

I agree with gmslave, also feeding times and how much of your nutrients you’re feeding them. Could be a simple over watering or nutrient lock out. I’d try a flush before feeding again, but that’s a wild guess. Don’t know much about the grow and the details

How are you growing, what are you growing in, hard to diagnose unless we have some info. Nutes used, how high ppm do you feed. At what ph? Soil or soiless?