Coco Seedlings slow and yellowing Overwatered/high Ph

fertilize every time... 10% runoff is essential to soilless context. do not let it sit in it's piss. 1.3-1.5EC concentration of fertilizer, not including any solutes that came in the water to start. ppms 120-130N 60p 180-200k 100+ Ca 50-75 Mg 100+ S good ballpark numbers.. don't have to be exact.. and, it would require some trial and error to refine for your local variables. the ratio is solid, the overall concentration is more likely what needs adjustment over time. what comes in your water may impact this slightly too.. so there's never a 1-size-fits all suggestion.. but there is a very good starting point, and this is it. you have a huge pot for a tiny plant, this causes problems too. I know "they" say not to transplant an auto, but the negativs caused by this context are far worse than the slim chance you shock the plant during transplant... I'm not sure if i've ever shocked a plant during transplant in a couple hundred tries, lol. Don't manhandle it and disturb the rootball and it'll be fine.. people mistake the roots feeling out new room to grow as "shock". It'll focus on that for a bit, typicaly, after a transplant. Water an entire column aroudn the plant all the way down -- runoff guarantees it, the 10% helps helps keep substrate at an appropriate equilibrium wiht nutrient content. Wait for top layer to dry, then repeat... as the plant grows increase the diameter of what you water... slightly larger than its canopy is good. once it properly fits teh pot size, it's the same procedure. soilless/hydro nutes of any integrity will be ph-balanced. Consider a different brand if this is not the case. Also, don't spend 5x more for somethign that says "pH Down" on the label.. simply go buy some 5% white distilled vinegar and a 3-5mL pipette if working with 2-4 gallons at a time (acetic acid doesn't impact nutrient balance). Again, people mistakenly think their ph-drift is due to the acid used, but it's more about a poorly made fertilizer product if it swings around like crazy. if it were buffered properly, all acids that fully disassociate when in solution will work well. Coco doesn't require more calcium, unless, again, the manufacturer fucked up. If properly buffered, it will not leach Ca++ cations. If it does, consider a different name brand coco coir, because they fucked up and eventually a bad batch will either severely hinder or kill plants. coco coir isn't magic. it's a fine substrate if prepared well by the maker or if you know how to properly buffer it, which is just a giant needless hassle, lol. i've used both promix and coco as a base for my soilless grows.. 3years and 2 years of each. I'm going back to promix (sphagnum peat moss base). I never had a batch bad enough to kill a plant, but i recently had a batch that defintiely hindered them the first 30 days before the nutes and coco got into equilibrium (buffered, in other words on the fly). It is more convenient to have it ready to use out of the bag compared to needing to mix promix with more perlite or similar, but i've had my scare and dropping it like a bad habit. coco is not magica. it has some severe drawbacks. Any substrate with proper amount of drainage improving amendments (like perlite, vermiculite etc) is nearly impossible to overwater, not just coco. Again, that is a misunderstanding.. usually born from the fact they didn't put enough perlite in with the coco alternatives. sphagnum peat needs a 1:1 ratio with perlite because it holds 150% more water per volume than coco. Coco only needs 2:1.. you can see how the math plays out here and balances out relative eto air/water mixture in the substrate. both ratios end up aroudn 50% air/water mix in the substrate, which is what matters, not the 'magic' of any absorbant material used. for the record, untreated sphagnum peat can be dangerous for plants if it is a "raw" form. it needs to be ph balanced, but at least it doesn't contain a shitload of Na+, like coco does if untreated. promix hp, bx etc are well made and ready to use, but need more perlite or similar added.