Cal/Mag. I promise. I wish I had the pics of my first 2 grows. They were IDENTICAL. It's an Mg def, but the plant needs C to effectively take up Mg, thus a cal/mag problem. I bet those leaves just crumble in your hand.
I thought (and was told by many knowledgeable people on several forums) that the problem was nute burn. So the second grow, I starved them. If ANYTHING there should have been a deficiency, but BAM, right in the middle to final weeks of flower, the same shit happened, I added Botanicares Cal-Mag the third grow and didn't have so much a a yellow tip.
Could be your camera, looks like dots, marks etc etc on lots of the leaves, reminds me of thrips but probably not in your case, just asking. How did it start all this? What ferts and how often etc etc Peace
Yes lots of times, i would think that it could be overferts, that makes 12ml of fert per litre yes/no? 4ml canna A, 4 mil canna B and 4 mil canna boost per litre = 12ml?
Re: how to flush... just ph some water and run it thru your coco to "flush" out everything thats in there. then feed it plain ph water a few times on your normal watering schedule. that'll clean it out. The go 1/4 to half strength with your normal nutes for a few days then back up to full by the end of the week. that should stop whatever is doing this. You probably have an overaccumulation of nutes in your coco or a ph issue, either way you need a flush. Its unreasonable to think a defieciency did that much damage in that short a period of time. You can include some cal/mag in your 1/4 strength if you think it might be that but cleaniing your medium is essential before you start adding things cause you could just be making it worse.
Plus, sounds like your ph meter won't give you a number, bad ph will lock nutes out, you can buy drops at pool/hydro/aquarium stores really cheap and they are extremely accurate. just get it a pee yellow color and your good.
Oh yer, no probs, just looked like mite or thrips, hmm funny to get that with an overfert problem, probably more like lockout, am out of my depths with the finer aspects of coco but will hopefully be using it soon. Peace