My substrate is very small crushed coral. My cal is 420 and alk is 7. The thing I have a problem with is the amount I have to add to keep those numbers. 34g tank and I add 60ml each daily. I have tried to stop dosing add calc how much each drops a day but I always end up back to 60ml each
60mL/day sounds quite excessive for such a small tank. Even when I ran a full blown SPS reef in a 24g nanocube my dosing was less than 15mL a day. Does the tank have a lot of mature SPS and clams?
I would get another test kit and retest with something different and/or more accurate. I recommend Red Sea, Salifert, or ELOS test lines.
I would love to tell you that "we know." But I think there are several causes mentioned above that all could be applicable. IME, it is bacterial build up (hypothesis of mine, not known fact) that can be solved simply. A Diamond watchman goby or the life. so go grab some sand sifting gobies, check basic water parem (do waterchange = solution for all bad things) and get this guy to stir things up: