First time grower - seedling help

[AtticGrower]

Started my first grow last week and I could use some advice.

I dropped the seeds 9 days ago and transferred to jiffy pellets 7 days ago. Kept them at 75 degrees and 90% RH until the roots poker through this Tuesday, where I transplanted them to pre-fertigated coco mix (70/30 coco to perlite) in solo cups at 400EC. I fertigated again the next morning and noticed that the runoffs from two of the 3 seedlings were in the 900EC range, with the 3rd and the 600s. The two that were in the 900s have not been growing as quickly and one is really struggling. I began fertigatong more frequently (2x/day with 40% runoff) and the runoff ECs came down to 725-750 today.

How are these seedlings looking considering I started germination 9 days ago? Am I doing the right things to recover the ones that are struggling, or is there something else I should be doing?

 

[DR.PNW]

Coco is a very specific medium and requires treatment that dirt does not.
It is a great middle ground between hydro and soil; the responsiveness of hydro but the buffer of soil.
With this in mind; it is hard on seedlings.
It most often requires flushing, pH balancing, and calcium buffering before use, especially with younger plants.
The EC is naturally high, that in mind;
In dirt;
300-500ppm is a safe range for seedlings and starter-potted plants.
700-1000ppm is the range for a large vegetative plant, and 1000-1500ppm for flowering.
In Coco it is better to consistently feed 300-700ppm and have your run off come out matching what you put in, with cal-mag at every feeding.
ie. 500ppm in, 500ppm out.
30-40% runoff should be your standard.
Don't forget to check your runoff pH.
Nice job using AC Infinity, they are a great company.