So Saturday night, I wrote down my remaining gallons as usual in tracking my water usage. Sunday night, the numbers were the same, 1422. Friday to Saturday, only 98 gallons used to get to 1422, and 24 hours later, 0 gallons used. Turned on a faucet, and the drop never appeared. Closed both valves on the triple tree, let everything come to a halt, then opened them up again. Now I have a drop, and water went down to 1417 by the time it all settled.

Hydrostatic lock? Or something else?