This is what our tank looks like so far....

[MitchM]

I would imagine that in the anaerobic zone of a mature and undisturbed DSB (I'm talking the bottom area...not where a tigertail resides) you'll have PH low enough to dissolve the sandbed.
There's your reactor, Em.
Didn't you tell me once that your tank Ca was higher than your waterchange Ca?

BC_grl, the page won't load for me...gateway times out or something :?

Mitch