COCO COIR Coco issues and recommendations?

[Tersky]

So i typically do hydro though i have done coco in the past with success. I got a new tent and 315 lec and have seedlings that are about a week since sprout. I use GH Flora trio and calmag for nutes. I have 2 Bruce banner # 3 and 2 Sour Diesel all in 3 gal fabric pots. I know i should have put them in a smaller container and transplanted later but the last time i transplanted it was a disaster so i potted in final pot to start with and have been doing strategic watering to force the roots to grow outwards. In the attached pic the Bruce Banner is on the left and the sour D is on the right. The Bruce Banner is in CYCO Coco Pearl and the sour d is in Mother Earth Coco Plus Perlite mix. Same everything except the perlite mix. The problem is that the Sour D is noticeably stunted. I have never had much luck with testing the runoff of coco so i have not done that but i have been feeding and watering within the 5.5 - 6.5 range being careful not to over water since they are seedlings. I have ordered the same coco mix i used in the past and am using with the bruce banner.

So here is the question. Should i re-pot the Sour D in the coco i know works when it gets here or does someone have any way to help me get these little bastards up and running. It's been a while since ive grown in coco and i have only done it a couple times so i need help lol. I feel much more confident with hydro but if you never try anything different you never learn, right? Also, how do you get accurate ph readings on testing the runoff in coco or can you even do so. Is there a trick to it? I've read some places not to bother with testing the runoff as it's not very accurate and that has been my experience as well. But then again, i could be doing it wrong lol. Any advice would be appreciated. Thanks!

[9fingerleafs]

check out https://www.cocoforcannabis.com/
i guess it could be the coco brand. never thought to measure coco runoff because theoretically coco is inert but if that coco has not been washed properly the issue could be that, wont get into the science but basically it takes calcium and releases potassium, this causes a deficiency and a nutrient lock due to the high mineral build up. you could flush those pots very well and then feed with plenty calmag good luck my friend

[Tersky]

Yeah i think i forgot to buffer the Mothers earth mix which is strange because i remembered to do it for the other mix. I think i was so excited that it had come in and i was finally going to get my new seeds started that i forgot to...well i flushed with ph'd RO and double cal mag and then added a little mild nutrient solution on top just to be sure it has everything it needs. hopefully they will come back strong. Trying to get back in the swing of it all and im just not as experienced with coco.

[9fingerleafs]

youll see its very forgiving