Some weird rust spots on fan leaves, any ideas?

Hey RIU, what's good?
So I am posting about a WWxBB grown from seed, that has been getting some odd rusting in the leaves. It is 33 days from seed, and I have been feeding it 1/2 strength botanicare pure grow, with calmag, mixed in water from my RO filter, which comes out 5-20 ppm. I ph the water to 6.3-6.5 , and feed when the pot feels rather light, and the soil dry. She is growing very fast, overall plant health looks good, so I trimmed off the problem leaves and took some pictures, what do you guys think it could be?

This one is the worst looking of the bunch.

And the rest look pretty mild compared to that one

With RO you will need calmag, that's a calcium deficiency.

Yep, I agree.

budman111 said:

With RO you will need calmag, that's a calcium deficiency.

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okay, so i've been using calmag, but i need to up the dose i suppose. I will do that next feeding, thanks.

Have you been using less than the recommended dosage?

bottle says 3-5ml / gallon, so I've been using the lower end of the scale, 3ml/
gallon, and I did one feeding with 4ml per gallon. I'm going to up it to the 5 next time though.

sookmahdook said:

bottle says 3-5ml / gallon, so I've been using the lower end of the scale, 3ml/
gallon, and I did one feeding with 4ml per gallon. I'm going to up it to the 5 next time though.

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go with the recommended dosage and foliar feed tonight 2ml per liter just ONCE because Calcium is really slow moving in the plant but a foliar will get back on track in no time.

Bud man..When u say foliar feed r u meaning to spray the plants..like if u were treating it with neem??

budman111 said:

go with the recommended dosage and foliar feed tonight 2ml per liter just ONCE because Calcium is really slow moving in the plant but a foliar will get back on track in no time.

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when you say tonight, you mean during lights out, correct? I will mix this up and do it shortly, as the lights went out about 30 mins ago

sookmahdook said:

when you say tonight, you mean during lights out, correct? I will mix this up and do it shortly, as the lights went out about 30 mins ago

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cool, now is the best time.

budman111 said:

cool, now is the best time.

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right on, just did what you recommended, thanks a lot for your input.

sookmahdook said:

right on, just did what you recommended, thanks a lot for your input.

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No probs, glad to help.