For all top off you can use a Kalk mix of 1-2 tsp(2 tsp makes it saturated) Kalk powder to one gallon of RO water. Test your calcium level now, you want near 400 ppm of calcium, then test again after a few days of using the Kalk to see if it is bringing the CA level up, once your at your desired level you can adjust the amount of Kalk to maintain that level. I highly recommend a Ph monitor so you can easily see what your Ph is doing at different times of the day/night and dosing. I have my Auto top off which flows through my Kalk reactor to only come on a few times a night when lights are out to keep the Ph more constant. I found if I left the ATO to top off whenever needed, day or night, my Ph would go a little higher than I was comfortable seeing (over 8.6). This is what works for my tank, every tank is different, just find what works for you and your tank. Good luck.
Wreck