Still nothing in the tank yet, but did unfortunately have something get out, and we were briefly able to enjoy empty water both in the tank and on the floor. Not too bad though. Was able to, at least temporarily, fix the leak pretty quickly, although not before certain hurtful words were willy-nilly being tossed around like "warped" and "corroded."
Turns out the blue circled part (is that a bulkhead or something?) was leaking and the water, instead of just spilling back into the sump, which seems logical, was doing a conga line across the top of the sump and escaping over the front and onto the floor.
Ordered some live rock from TBS which should be here in a week or so. Hopefully limited excitement until then.