Tap water is the number one killer of moss and nobody wants to hear it. That chlorine and calcium builds up in the moss and there's no coming back from it once it crusts over. Distilled is fine but rainwater is free and the moss loves it. You probably didn't even need to move the tank, the water was doing most of the damage. Portland water isn't even that hard compared to a lot of places, so this would've happened to you anywhere.

Killed the main in 20 seconds? Thats the right call but 4 feet from the panel means that pipe was prob already running right next to where you had to drill, not really bad luck. Carry a couple sharkbite caps in 1/2 and 3/4, theyre cheap and save your ass.

I read a thing once about how cheap digital scales use load cells that can get permanently bent if you drop them or press too hard, and after that they just read wrong forever. Even a little bump on the counter can throw them off, so the drift happens slow and you never catch it. Best trick I heard is weighing a few coins or a cup of water every few weeks, since water is 1 gram per milliliter and that stays the same no matter what.