rust color spots "help"

its 4 weeks now into flowering and i did my flush of the plaints for the last 2 weeks and 2 days later this happens to the plaint can anyone tell me what might of happened here

Was The Water Cold? Or To Warm? Possible Nutes Locking Up In The Soil. Possible Burn? You Used 3 Times As Much Water As Soil? Looks Like A Burn To Me Go Slow With Nutes Always Slow Slow Slow

yes straight tap water and it was warm 3 times soil and drained it. if nutes was the prob they must have been in the soil since the last time i gave nutes i have only given these guys rain water since birth no tap water.