Hate to say it, but it sounds like you've got a massive ionic imbalance. Water changes are the best way to cure it.
If you can't raise alk with buffer, then water changes may be your only practical solution. The problem is that for Ca to come down naturally, you need calcification in the system. With low alk, you won't get as much calcification. So your Ca won't come down. Nor will your calcifying livestock grow well or be happy.
Two words: water change.
It comes to a point where the supplements quit working. I take it you haven't been doing regular water changes. Water changes dilute ionic imbalances. Over time, adding a bunch of chemicals to keep thing in balance, while not diluting their deliterious effects with water changes, will get you into trouble. That's where you are now.
If you haven't done water changes in the past, now's the time to suck it up and do them.
I post pretty regularly on the biomineral threads and often can come up with an "easy way out" but I couldn't and wouldn't recommend anything but water changes in your case.