I use ESV 2 part and I am very happy with the results. I would highly recommend it. It also helps keep mg stable, and also doses minor trace elements too.
How big is your tank? It doesn't look like you are using up a lot of alk. My tank drops that low in a single day if I don't dose. I would start with 1ml a day and test the same time every day and monitor it for at least a week. If you notice your alk dropping still, than up the dose to 2ml a day. Rinse and repeat until you reach your target area where your alk is staying constant at the desired number.
That's how I started doing it, and it worked out perfect. I have a 42g and I started dosing 3ml a day, and now I am at 12ml a day to keep my alk around 7.8 to 8
As long as you dose the 2 part in equal amounts your Ca and Mg should also stay stable. I don't test for Ca and Mg anymore, but every time I would they would always be the same. I also heard that if you do not dose this 2 part in equal amounts, your parameters may give you funky numbers. I have dosed a little more of the Ca solution some times with no adverse effects (about 2ml more than the Alk component) in an attempt to increase my Ca. But I stopped and just continued to do them in equal parts.
Only thing I would like to get more information on regarding this 2 part is what the actual numbers in ppm are that it increases it in case I decide to change it...