Why is new growth looking like this?

Well I think 001100 covered everything. I’ll always say check your PH first because it matters more than anything when trying to apply corrections. Then again I grow DWC.

More than a few things can caust chlorosis in new growth, which is what i see here. So, there's not "1" answer for you at this point. If you recently switched to a bro-science or instructed "flower" formula, it's likely too much P or K. This would cause skinny new growth (fingers) and chlrosis on new growth - so, definitely possible. Too little S is another option, but should be able to eliminate that by cross-referencing symptoms. Is the bottom of the apical meristem (trunk) 'corky?' Are there red or purple streaks in the stems (!! Not leaf petioles, stems only)? Also the chlorosis would progress inside out which is odd and would stand out, so i doubt it is low S. Some trace elements can cause chlorosis in new growth, but if your fertilizer is worth anything, should have all of this. Which leaves pH. IF pH is too far off from 5.8-6.2, more so on low side, you'll run into some lockout, but this would usually impact Ca first and higher chance of a smorgasborg of symptoms because pH balance will at some point affect multiple nutrients. Easy to rule out, like S. I'd let this progress a bit more, as long as it is a slow progression. Be certain of what the symptoms tell you. for vege i'd suggest somethign like 120-130 N 40-60 P 180ish K 100+ Ca 75-80 Mg 100-110 S This would be a fairly low concentration overall but well-balanced as far as resulting availability for the plant to grab and use. In flower, drop N to 90-100. Might need to drop down near 1.2ec late flower if darkness creeps in. But, any symptom you see will be rare and slow-moving with easily diagnosed symptoms and minimal adjustments needed to get it right. Overall concentration will be more a function of VPD and other local variables, but the ratios of nutes is solid. Your tap water may cause a few deviations. However, when i switched from 300ppm hard water to softened water, I didn't have to change anything, fwiw. This isn't 'my' formula. It is one used by many professional AG companies that sell a 'hydro' system of nutrients -- ~3 parts should be sufficient. religious 10% runoff waste water is absolutely integral to a soilless grow running flawlessly. if neglecting that, it could be the cause of what you see. fertilizing isn't about what you did yesterday or even last week. It's the culmination of your behaviour since that plant has inhabited that pot. giving too much or too little can sometimes take months to show itself. Despite common belief, plants are not significantly more picky in bloom. More often problems seen in flower are due to poor fertilization habits in vege phase, but that would mean taking accountability for a problem rather than blaming it on extrernal sources, which most egos will not allow. It ain't foie gras. You can't force a square peg through a round hole where L=D. Goldilocks zone is what you want.. not more, more more. ---------- Mg deficiency is interveinal chlorosis with rusty necrotic spots. I don't see this hear, also it would normally start mid or lower plant because it's at least partially mobile. I don't see this. Calcium deficiency is just spots, and i don't see that. Adding calcium or magnesium probably won't improve anything. Coco does not require more calcium than other soilless substrates that should be devoid of nutrients or simply not impact them in the case of 'good' coco coir. It does not change any biological process in the plant, therefore the same levels of Ca will work with coco as anything else. The pitfall with coco is that it requires buffering not to initially leach cations (like Ca++) from your fertilizer. Even so, this is a temporary thing and will eventualyl reach an equilibrium where nothing is lost or gained as far as interaction with fertilizer. Not something you want to power through. It;s one of the dangers few speak about when dealing with coco. Unprocessed coco can kill plants very easily with Na+ or releasing a shit ton of K because it wasn't properly buffered for use with plants. I've never had to change my formual as i switched from sphagnum peat moss base to coco coir and back to sphagnum peat moss. the only thing that differes is the amount of perlite or similar you should add, because coco coir retains less water by comparison (33% perlite vs 50% in sphagnum peat moss). 100-120ppm of Ca should be plenty as part of a well-balanced 1.3-1.5EC fertilizer. If providing roughly that and having issues, it's a sign that you are too high in something else that can inhibit Calcium uptake or use in the plant. How much you tap water adds may influence the exact amount you need to add. soilless requires 100% of nutritional needs at all times. You'll need to drop N fairly early in flower and reduce overall concentration mid-to-late flower, but otherwise a good consistent formula will be fine. Religiously get 10% runoff to ensure no buildup of nutes occur. this eliminates one possibility each time you see a problem -- it will never be buildup but rather simply feeding too much of one thing in your formula.. it won't build up in the substrate but it can be over-provided. Flushing should never be required except for utter catastrophe.

Up the feed mate. Sensi coco has enough calmag in to cover most of the time. Especially at your stage. But your using very little going off the dairy. I start on 2ml per litre in coco.

Magnesium deficiency. Add some cal/mag to your fertilizer line up or increase the doage if already using one. Symptoms will take 10-14 days before they disappear.............new growth should be ok if you add/increase the cal/mag. When growing in coco coir, you need to use extra cal/mag from virtually day one.