All well until week 2 then this (yellowing)up to p...

Well, they look super overfed / it looks like a nutrient lockout. This means you gave so much fertilizer the plant can't uptake anything at all. (im assuming because of the dark green leaves and the burned tips" I know you just wan't them to be healthy and grow strong, just slow down, only water with pH water for a while. and PLEASE buy some Neem oil with emulsifier and use 10ml / L to water your plants, will kill ALL insects without doing harm to anything else, its biological, don't worry. Also the soil looks a bit dry in the pictures, if it's really dry the root's can burn when using synthetic nutrients Well i hope you will fix it, good luck! (:

Your "numbers" ain't fine.............plants are waaaaaay over fed and starting to be burned. It is not a potassium deficiency, it is nitrogen toxicity.

Usually when it progresses around the serated tips, it's k-deficiency. looks like you got gnat larva eating the roots, too. also, don't think top down. it;s not about what you chose to do, it's what works for the plants. if 1 of 4 plants is having an issue with your fertilizer, it is the formula that is at fault. it is out of balance and only some plants can mitigate what is out of balance. when you see deficiencies or toxicities arise, it is the formula used that caused it. it is definitely more than possible to give what is needed in a way that works for 99% of plants. it's worth the effort to find through trial and error. in soilless it's a hell of a lot less error along the way to that end. every soil is a bit different. soil fertilizers don't always come with gauranteed analysis, either. inevitable with a bunch of unknowns...