Matt, thanks for the comments. I'm using Oceanic salt, and you are correct - I need to test it for carbonate hardness!

The tank/system is about 700g capacity and has been up & running since about October. I "seeded" it with LR and some sand from my 125g, but still a very immature system.

I'll check the salt mix, then think about a little buffer. A slightly higher dKH and Ca around 400-450 is where I would like to see it!