The reason the excess water draining from the pot is coming out at a significantly lower PH is because something in your medium is causing that. You'll need to provide some additional information about your growing medium, plants, and environment before I can attempt to provide feedback.
One thing you can do (regardless if growing in soil or coco) is add beneficial microbes and create a living soil. This is what took my growing to the next level, seriously.
What microbes do is feed on the nutrients in your soil and break them down - having bacteria colonies that do so allow your plant to take-in nutrients at a wider range of PH levels. I use Recharge by RealGrowers but there are other company's with microbe packages as well.
When your PH is off it keeps the plants from absorbing certain nutrients. For example you are having problems with Ca. In soil Ca cannot be absorbed in PH conditions under 6.2. You can feed all the Ca in the world, but the plant will not absorb it.
The other thing you can do is flush the plant(s) with a light nutrient mix, say 1/4 of what you normally feed. But you'll want to PH the water to (_____ amount) until the runoff is the same as it was going in. I've only done this with coco so i'm not sure how well it would work with soil.
As far as how much calmag to use... gosh that's so arbitrary. I typically feed @ 3-5ML/ per gallon but I also use mostly RO water in coco so it's kind of necessary. There's a lot of people on this forum who claim they don't use it and don't have issues, but that's not the case for me.
