Thought It Was Magnesium Def Not Sure Now

looks liek nitrogen deficiency... despite a common and loud urban myth, the plant needs a good amount of N in bloom too. the one plant not exhibiting this is overfed. you will need a different formula for this plant. never think in terms of 'but i gave it the same feed' -- it clearly doens't matter. some plants are picky. the better your formula is the less you'll need a 2nd misture for an oddball plant. the good thing here is you said it was a runt.. could just be a slow growing plant that you are feeding like a normal growth rate, therefore nutes will ineivitably build up in that context.

When a plant shows deficiency and toxicity at same time like your plants look. It is a build up of salts from old fertilizer with not enough run off. This causes nasty ph swings. I have had this issue, and this looks a whole lot like your problem. The ro water did you no justice going to it here.

All the pictures except the last one looks like it's lacking nutrition, but as stork pointed out that last picture looks like over fertilising. They are different plants showing completely different fertiliser problems. My guess would be the over green plants ph is in the correct range and using all available nutrition which has slightly to much nitrogen. The other pictures I'd say the ph is out of wack in the grow medium and it's not taking any nutrition.

One looks like over-fertilisation other looks like under-fertilisation am lost 😵🤯