Is this nitrogen deficiency? Should I change the soil?

As long as the soil is above 5.5 and below pH 7.5, true nutrient "lock out" will not occur and growing in soil anywhere from 6.5 to 7.2 is fine. Trying to remove soil and replanting them into different soil would cause so much stress to your plants, that they might just stop growing all together. Ask me how I know! They definitely won't like it and you are much better leaving them as is and working on a slow recovery process, as trying to achieve a "quick fix" will undoubtedly cause more or worse problems than if you had just left them alone. Most of the products you are using for feeding your plants are basically supplements and not fertilizers/complete nutrients in the true sense, Rezin is a "enhancer" with no N/P/K. Ocean Magic is another supplement with no nitrogen or potassium, just phosphorous at 5%. Pro-Cal is obviously a cal/mag supplement, at 1.5 and 0.5% respectively and 2.0% nitrogen and no potassium or phosphorous. Medi one is your only real fertilizer, but at 4/3/3, it isn't going to set the world on fire. Even mixing these you end up with a N/P/K ratio of 6/8/3 which is no where near enough potassium, adequate phosphorous and nearly adequate nitrogen. I would be looking to add a product with a touch more nitrogen, a good supply of trace elements and a lot more potassium, something like GP3 from the same manufacturer of what you already have or go through the list of Green Planets' "base nutrients" and you should find a product that will help your plants thrive, "Back Country Blend-Grow" being another that may help. So, leave your soil as it is now, there is no easy or fast way of reducing pH without stressing your plants and give them some extra base nutrients and they should pick up soon enough. Oh, a bit more water too, they look a bit thirsty to me. Watering deeply to run off will help prevent nutrient salts from building up in the soil to toxic levels and your plants need an evenly moist substrate for good root development. It is far better to deep water once in a while and let the soil dry out again before deep watering again, than it is to give little/medium water frequently. Also, water your pots from edge to edge and not just in the middle, the roots will want to be at the edges. Re-water once the top inch or so has dried out. Try to have an evenly moist soil, not too dry and not too wet. It is a bit of a learning curve, but once mastered, will be easy to understand. Hope this helps,......... Organoman.