I figure the roots are mainly centered in the promix atm...only a couple day since transplant...the solution I pour if I soak the whole pot will build up in the rest of the cocoon because the roots wont be absorbing it since they’re not there...that’s why I’m not soaking whole pot...am I wrong to do this and I should soak whole pot even if just transplanted?
Yes you need to soak the whole pot or at least that's the way I've always done it in ProMix and I'm pretty sure you need to that in coco too. I usually start clones or seedlings in tiny 9-hole seedling pots then go to a 2L pot then a 4gal pot and always soak the new pot good at transplant time. I won't feed every time tho for the same reason. The roots haven't filled the pot yet so areas they haven't grown are still holding nutes. I'll use just water for maybe the first few waterings so may not feed for a month after moving a relatively small plant to a large pot.
With the ProMix I rarely get any runoff so when the plant is small the bottom half may still be wet while I can dig down a few inches and it's dry tho moisture wicks up from below. This is where guys run into root rot problems. That moist bottom has no oxygen in it and bad bacteria can take over and get rot started. Even going from a 2L to a 4gal pot I generally have roots poking out the drain holes in 5 days or so. A 2" plant can have a foot long root so most peeps water again when the top inch or so is dry when the plant has roots down in the wet area already. If you just water a little at a time then the roots end up hitting dry media and dying. It's like root pruning when you don't want it to.
You are correct in saying that nutes will build up in the pots if you feed all the time without substantial runoff to flush out the old stuff. Same thing happens with high ppm tap water. Most of the minerals in the water add up and create toxic conditions in the pots. That helps lead up to toxic salts buildup that I see so often in the forums and with my own plants tho I use RO water only. We have low RH here so the plants drink a lot more and pull up more minerals than they can process so it builds up in the leaves and usually shows up about mid-flower with older leaves going all brown/yellow all over and turning crispy. That can work it's way up to the buds eventually and once started can't be stopped even with heavy flushing tho flushing will slow the progress.
Like I said, you should search the forums for more info about coco as I tried it once almost 20 years ago and didn't like it but I was doing it all wrong with crappy coco that surely needed to be rinsed well before use but I knew nothing about it at the time. Cheap shit that came in a hard block and was likely loaded with salt. Wasn't even a label on the block I bought just a felt marker saying 2kg coco coir. Still have half of it around here somewhere and should try rinsing some then check the ppm of the water.
