Help needed, coco/perlite grow, please look at pics

Hope i can get some advice, can anyone tell me whats wrong with my plant, The 1st leaves it grew are turning yellow and the lower leaves look light green, is it nitrogen def?
Is 600ppm ok for a 4 week old plant from seed or should i be higher than that now?
Also if using coco a/b nutes do i need to add any calmag?

Plant is 4 weeks old tomorrow
Temp: 77 day 66 night
Light: T5HO 4x24w bulbs on 20/4 schedule
11L air pot with 50/50 coco/perlite
Nutes: Canna coco 600ppm (700 scale) 5.8ph - approx 2 litres every 3 days
Run off: 660ppm 6.5ph
(My water from the tap is: 110ppm 7.8ph)

Bump up the food bro looks hungry. I don't use canna so don't want to say bump up a lot as I don't how the line works but def could use some more food. Ph is fine at 5.8 and I believe I watched a clip on canna nutes the coco ones that they have good cal mag in the bases.

I would also consider not running the temp so cold at night, too cold of temperatures can start to cause withering. I had my first setup at 65 off and 75 on, ended up getting frost.

Thanks, that was a month ago but she looks fine now

Boom...! She got big dude

I see Mg def in the folded upper leaves. Looks like heat stress but if youre temps are OK, I say Mg.

I dont think it is a case of underfeeding. 600ppm is high to me and my Hanna meter. The fact that your runoff is higher is a pretty clear sign that the plant isn't able to use all of the food youre giving her.

You probably have salt buildup which leads to pH issues, lockouts, etc.

The last thing you want to do is up the ppm's. Here is an occasion where I might flush and start with less concentrated but more frequent feedings.

Also noticed youre using 11 liter pots. IMO that is way too big for a plant that size especially in coco. You dont need more than 4 liters and you should end there, transplanting only when roots have filled the previous pot. All of that coco soaked in high levels of fertilizer and the plant doesnt have the root system to use it all. So it builds up and causes problems. Then everyone goes straight for X deficiency and you make it worse by increasing the buildup.

To really get the most out of coco, small pots (only as big as the root system) and frequent light feedings are where it shines.

Yeah its been a bit warm in the uk for the last few weeks and temps did get a little higher than they should have been, getting up to 90f at times. I am using magne-cal + with the food and i'm at 1000ppm at the min just started 12/12 yesterday but i may up the dosage on the magne-cal as it does look a little mg def still.