Dude,

Your fuge light, that on a reverse cycle?

I'd definitely add some kalk, get an iv line set up and rig it to a container with some kalk mix. You could also use some two part...

I think if your calcium is up to 400 or so your ph should be a bit higher. I wouldn't attempt to try to raise your calcium using kalk. Were I in the same position I think I'd try a few water changes until my calcium is at the right level and then begin dosing kalk to maintain it... with weekly water changes. Small tanks are tricky.