Rust spots after switching from mh to hps

1000w hps. Just switched from mh 2 days ago
5X5 gorilla
Growing in botanicare coco in prunex pots
Advanced nutes sensi grow coco at 16ml a gallon using ro water. Comes out about 1040ppm. This only seems to be on the fan leaves and appeared overnight. This is my 3rd grow and it happens everytime I switch to HPS getting ready to flower. Drives me nuts, plants all look great until I'm about to flower and wham. This crap. Any help would be greatly appreciated.

using r/o water,not supplementing cal/mag

chuck estevez said:

using r/o water,not supplementing cal/mag

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I thought that supposedly with the COCO version of sensi grow it wasnt needed to supplement extra call mag as it has it in it?

MuppetMower182 said:

I thought that supposedly with the COCO version of sensi grow it wasnt needed to supplement extra call mag as it has it in it?

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for normal water, but r/o has none, you need to add some occaisionally

chuck estevez said:

for normal water, but r/o has none, you need to add some occaisionally

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i spoke with an advanced rep and he seems to think its caused by nutrient lockout, saying i should flush and it would be fine. I asked him if the coco version has enough cal mag for ro and he said it shouldnt be a problem. I will also try your recommendation and hope one of them fixes the problem.

edit: Runoff ppm was at 1700. I dont know what caused such a horrible build up but flushing down to 6-900 ppm with rro water