Just because you are using the same nutes as your friend does not mean you have the same growing conditions or issues, success or failures.
Those plants are having problems uptaking nutes! Ca might be possible cause of those rust spots, but so is a K issue and Mg issue. Another thing issues with Calcium are different then issues with Magnesium. The rust spots will generally show up on older or middle aged leaves first with a Mg problem. Mg issues often take a little while longer to show up in a plants life cycle. Mg issues could be curled, canoed leaves in your canopy and a tiger strip look with yellowed/yellowing edges, yet a green striped center to the leaf(green along the veins). Your leaves look like they are well on the way to having a Mg issue as well as Ca and overall uptake issue!! The issues with the leaves could or often are an extension of something in the roots or their development.
We need to make sure your plants are uptaking/absorbing nutes properly from the root zone. This is what lead to proper, explosive cannabis growth.
Did the tips, margins and then the leaves develop spots then yellow?
The purple color of those stems indicate an issue uptaking nutes as well. RO water can help lead to some Ca issues in young plants if the nutes used are not balanced in the correct ratios for the feeding! Fixing and or understanding the uptake issue is a must, not just throwing Cal/Mg at the plants. Sometimes this can even make things worse. There could be many causes for the problem of nutrient uptake, including and not limited to, pests, disease, root issues, climate.....
I like Ca to be around .8% or so the total N in flower, meaning if I was nuting with a formula that had a ppm of 120 for the N then the Ca would be around 96 ppm of Ca. You need more Ca if you recirculate to help buffer the nutes. Less Ca if you drain to waste.
You need to understand fully the exact ppm nutrient profile, as best you can, that you are feeding the plants in order to best interpret their physical problems and relate to the language of the plants as they communicate their needs.
Please let me know the exact ml per gallon of GH G/M/B and Cal/Mg that you are using and I will figure out your profile. What is the size of your reso? Can you post picks of the whole plant?
With GH I would consider a profile of 5 micro, 5 bloom and 6.5 grow with the use of epson salts at a ratio of 1.25 grams per gallon once you flip to 12/12. I would change the reso often, adding back water only for top offs and keeping the ph adjusted to 5.7. The 5micro, 5bloom, 6.5gro will lead to a ppm breakdown of..
N=121 (this is a touch high if you use a Nitric acid based ph down product)
P=42 (this goes up when you use most ph down products, like gh)
K=161
Mg=65
S=57
Ca=82
No more Lucas....
I try to grow in flower with a N-P-K ppm ratio of 3-1-4, something closer to the ratios found in tissue samples of actual weed plants that have now been conducted...
It sounds stupid, but you can add Ca by using your regular tap water(if you know the amount of Ca in your water and its not too high, some people have crazy amounts of Ca in their water), without adjusting your N profile.
CaMg always adjusts the N ratio, which you might want to have a little more control over. I always treat Mg problems with epsom salt dissolved in a little water and added to the reso. This adds S which in most cases is a good thing! Sulphur is what makes your plants realize their full potential for the development of their aromas. Add more ppm of S to your nute mix and the plants will wreak....
We need to get your plants flushed out and on a nute profile that you at least know what you are feeding them...
Here is a shot of a K issue first on the big fan leaf, this dude starved his plant of K by accident and this is what happend... the second shot is classic Mg and Ca issue on a young clone... The third shot is a Slight Mg issue creeping in! Notice the slight yellowing starting from the edges of the leaves, notice closer the little tip of each seration and how they have yellowed first and most intensly, and how the yellow discoloration is begining to run into the leaf.
You should take pictures of your plants everyday and save them to catalogue the progression of the plants. You will learn a lot! Take pictures of many of the leaves that you remove(not every one, but a lot), track the nute issues, and deficiencies! Learn the language of your plants, they are screaming at you for the most part, the leaves always tell you what the plant needs.....So many growers have hungry plants so late in flower so many deficiencies...but that is another discussion..
