Yellow Leaf Dots Spreading Completely Over Some Leaves (It's not spider mites)

I've been fighting this problem as well, and haven't found the solution yet.
Please let me know if the Cal-Mag takes care of things. I'm on grow 2 and can't figure out where/how this issue begins.:(

Cal mag helped. Happens more in winter than summer and is also more frequent on one species over another. Does not seem to effect anything in long run and I have quit worrying about it. Sometimes it happens, sometimes not.

Left RO water about a month ago and cut down on cal mag and seems fine.....

It looks exactly like rust. Eagle 20 or Bayer disease control are the only things that helps. Once you get rust in your room its almost impossible to get rid of. I have bleached(12 oz a gal) and used ammonium chloride between grows and it always comes back in the end. What I have been doing is spraying once in veg once day 1 flower and once 1 week into flower. I normally see the 1st signs at day 35 of flower. It is a very slow moving fungus. What I have observed it only effects fan leaves. I have not seen any major decrease if any at all as long as you control it. Keeps your nutes a little higher than normal. As soon as you start to flush the whole room will look like Autumn in a few days.

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It looks exactly like rust. Eagle 20 or Bayer disease control are the only things that helps.

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thx for the insightful info bud. I'll check those products out. Can u use them in a room with plants in full bloom? I'm thinking sulfur bombing is way easier and probably cheaper if I build my own burner, but I definitely do not want to affect buds of plants just a few weeks away from finishing. I'm surprised that u don't use sulfur however.

I would not spray past 10 days in flower. Sulpher is probly your best bet far along into flower, it should slow it down. Spray your next batch of babies with the e20 or bayer. The reason I don't use sulpher is for 2 reasons 1. It does not work even half as well as the other options if used as a preventitive before the issue even arises. and 2 its a pain in the ass for me because my 2 rooms share a ventilation system so I have to shut down both rooms for 4-5 hours twice a week for it to be effective. Then air them out it turns into an all day job.