Burmeseanswered grow question 3 years ago Hi there, IMO those rusty spots could be either Calcium lock out or deficiency.Give a slight touch of cal-mag couldn't be wrong. Before you do anything, make sure your water pH, ppm(EC) and run off are in corrected range.If you are growing in soil, keep your pH around 6.0~6.5 for both of your water and run off.Also in soil,the less nutrient the better to prevent lockout.Happy Growing... ✌️