Welcome D D !

From the picture I think they have some kind of nutrition deficiency. Purple stem often are due to inability of the plant to uptake P.

Yellowing can be due to insufficient N and MG.

I have a couple of questions:

-- what kind of growing medium are you using ? (soil less ? garden soil, compost ???)

-- How often do you water your plants ?

--- How often do you fertilize your plants ?

--- what kind fertilizers are you using ? (analysis , please !)

Wait on for more comments.

Sey

Thank you for your reply. I've used a multi purpose compost purchased from a garden store and planted straight into it. I only water when the soil feels dry, I put my finger in the soil to check.

I watered the compost with a seaweed fertiliser just before I transplanted the plants, and I sprayed them a couple of days ago with more seaweed fertiliser in the hope to get rid of the issue.

I never fertiliser them when I speed the seeds, would that have Been a problem?

Looks like an environmental problem vs. a physiological one to me. Perhaps you burnt them with spraying fertilizer onto the leaves. That would be my guess with knowing the provided info.

shouldn't really use compost in a container as you could have drainage issues, use a potting mix which is specifically formulated for container use. seedlings do not need much fertilizer, i hope you gave them a weak solution.

the compost does look very wet, my guess is that it is waterlogged and the plant s drowning.

by the way, blossom end rot has nothing to do with it.

I'd get an analysis on the compost. Some serious imbalance appears to be in the soil. Some trace minerals may be at excessive levels and causing toxicity.

Can it be fixed and the plants salvaged? Yes. Get them out of the compost and potted in to a good soil-less potting mix, feed them a well-balanced N-P-K fertilizer to give them the nutrients they have been deprived of (seaweed is almost totally potassium and they need nitrogen instead), and reduce your watering.

Container growing is totally different from in-ground growing and things that work in the ground do not work in containers.

Dave