Looks like early nutrition burn. Always have run off of 20 percent to stop old chemicals from building up in soil. Check ph and TDS of run off. With using the bloom complex, you should not be deficient unless your going light. Would guess your substrate ph is getting out of line and causing issues. Good luck and happy growing 🌲🌲👊
Yes, this is a pk deficiency by the looks of it. You are 3 weeks into flowering and potassium is needed in abundance now. Up your flowering nutrient mixture next feed should fix it.