3 week old seedlings - first "true leaves" yellow - HELP?!

Hello all, new to posting, but long time lurker here.

I have 3 three-week old seedlings growing in 4 inch rockwool cubes under a 200 watt CFL. I am using the 3 part Advanced Nutrients formula, equal parts of each, with a strength of 400 ppm (measured with Hana TDS/PH meter).

I also added some H2O2 to the nutrient solution.

After accidentally letting the cubes over-dry, my plants drooped severely. I have been able to bring 2 of them back, but now their first set of leaves is COMPLETELY yellow, and look like they are drying up. Meanwhile, the fresher sets of small leaves are still green, but growth looks like it has stopped.

I have continued feeding a small amount once a day, keeping the cubes moist.

Will my plants ever come back to full strength? Should I just start over? Do I need to be feeding them differently? More nutrients? Less? Should I have waited to place them in 4 inch cubes? (did that after the 1 inch cubes were drying out too fast) Does that even matter?

Help!

And THANK YOU!

I think I figured this out...Once I placed the rooting cubes into the 4 inch blocks, my roots were too hot and had less chance to breath...at 87 degrees, I think this was causing the yeloowing of the leaves. After several days of lowered root temps and adding a healthy amount of H2O2 to the nutes, growth is resuming...

Or maybe you just had a nitrogen def and the plant was using its reserves from the cotyledons and true leaves. And your feeding fixed it.

yellow leaves could be a number of things.

can the plant die with yellow leafs i have yellow tips on my plant its nearly 3 weeks old i have taken it away from the lamp because i think its the nitrogen burning will it cure up or not?

money drugs power said:

can the plant die with yellow leafs i have yellow tips on my plant its nearly 3 weeks old i have taken it away from the lamp because i think its the nitrogen burning will it cure up or not?

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Yes, eventually, but it can also live with yellow leaves. Couldnt give you any advice without seeing pics and knowing the what you been giving it for nutes.

my plant is allright now i think it was a little burn ........anyway its nearly 4weeks old not very tall at all 17cm and its starting to show pistils and i am scared is this bad or wot?