There is more than one thing going on here, but almost all tap water has enough calmag to maintain a plant in a peat based soil. Adding some to your soil mix is still fine as long as you add the correct amount. Adding additional calmag to tap water is not necessary.
FF trio is not inherently hot, but it can be when mixed with the FF soils. I am not familiar with the soil you used, but if it’s a fairly standard peat mix then it’s probably pretty low EC value compared to FFOF or even FFHF. Which means your primary nutrients are coming from the trio, and probably not much from the soil.
There could be a lot of other issues that are causing the problems , but the way the yellowing is progressing looks like N deficiency, which usually starts at the bottom and and works it way up. Overfeeding will usually start closer to the top and cause more burning and curling. Lockout can cause the appearance of both of these symptoms at the same time sometimes making diagnosis difficult.
If you overwatered during veg that could have slowed root development and now be causing the slower growth and appearance of nutrient burn, there are just so many factors to consider. Most of the issues I see here are related to over feeding causing nutrient burn or over watering causing slow growth, and often both. Your problem does not appear to be quite so straight forward and will require a more careful diagnosis.
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