Rust Spots on Large Fan Leaves

5 weeks Veg
1st week into Flower
600w HPS 18" from top Fan Leaves in a Grow Lab 80L
Using GH Flora Series Nutes
RO Filtered Water 23 PPM
PH in current Reservoir 6.1
Nutrient Reservoir 1130 PPM
Temps 75 - 83 F.
FIM'ed at 2 weeks into Veg
RainForest 66
Bag Seed

Any input on this problem would be greatly appreciated. This is my first grow and first post here on RIU so hello everybody. First noticed this problem 3 days after my first reservoir change using RO Water. About 2 weeks ago now. Never had this issue prior. I suspect its a calcium deficiency due to the RO water, but Im no expert. Its what Ive been able to gather from the few posts relating to this issue. Spots only appear on top fan leaves and no other issues with the plant. Perky and healthy. Anything I should be worried about? Any input from someone with a similar issues or a VET with a few grows under his belt?

looks like a calcium or magnesium def im not 100% so wait and see if any1 agrees with me...

Appreciate the input... So far I agree with you but what do I know... Im a NOOB

It looks like ca def, hard to tell with the reflection. The problem is how is it becoming deficient. I run 8 ml per gallon of micro and that takes care of deficiencies on 99% of strains indica or sativa w/o over doing it and causing lockout... If u used more than 8ml, it is probably lockout and u need to dump the res and start over with fresh ro and nutes, if u used less than that add more... 200ppm should do it in that case.

If u want, on ur next resevoir, try using 8ml of micro and 16ml of bloom per gallon w/o using grow. Its called Lucas formula and when u use it u dont have to change the resevoir for the whole grow, u just keep on adding nutes and RO water. Let me know if u want to try it out, I will get u the addback formula.

By the way, nice job on keeping track of whats important. Its good to see a so called Noob checking PH and PPM and posting as soon as they spot the problem w/o trying to go nuts and guess. Good job!

First off....congrats on the first grow, they look pretty damn nice, of course besides the spots.

now...Ca deficiency usually starts on the new leaves first, not the old fan leaves. what you have appears to be a magnesium deficiency. early stages. generally this is cured by using 7/8ml/gal of Cal-Mag (CM). it's not very bad yet. I've seen recoveries from much worse.

just my 2 cents

also, as phelps said, thank you for not being an impatient noob and trying to guess at it and hope your right, that's the way to screw up fast.

Yea I ordered up some cal-mag and as soon as I get it, Ill start from scratch. When I change the reservoir, I first check and balance my PH to 6.0 and run pure water for 24 hrs to flush it. Then add the nutes at 50%, check the PPM 12 hrs or so later and then add the remaining per the feeding schedule. So far its worked. Some advice Ive picked up on RIU. Prevents nute lockout and so far so good until this came alone.


So is it common knowledge when using a RO water supply? To add something to make up for the Cal and Mag filtered out of the water source?

Seems to be the case but no one seems to want to go out on a limb and actually state it from experience. Just curious to know and once again, appreciate any and all input.

Im in soil, have this same problem, only with one strain. I will definately get cal mag at the store tmrw when I get soil. This thread may be old I google searched to get it. Any results yet after adding calmag?