different strains!

I wouldn't abandon either of the small plants yet unless you absolutely need to...for space or something else. Being topped in week 3 they could just be experiencing a lag and need a bit of recovery time. There's also the problem that all plants grow differently, even amongst the same seed batch or strain. Even if you decided to flip the plants today they could both grow 2 nice solid colas. If you continued to see weakness or traits you don't like then I could understand removing them over wasting time/nutrients/ light and space from the other better plants. But I would definitely hold off for several more weeks....perhaps a nice dose of a silica product and kelp extract as those can be great plant tonics and silica just makes stronger healthier plants. Happy growing friend, I hope they'll pleasantly surprise you anytime now. ✌️

You might be over doing it with your plants on the feed. I forget whether it's P or K but it's something like...A potassium toxicity will show up as a Mg deficiency. So you when you added the extra calmag without flushing first it probably made it worse. You've done the right thing with the flush. I'd start at 1/4 strength nutes and work your way back up. I don't know much about those kinda nutes but 11.65ml/l seems crazy high. I'm at 10 but half of my feed is pure calcium and it gets eaten up in half a day which leaves my ppm average at 450. Anything over 800 is overkill imo.