Hmmm, You're right, doing a search for "outbox" comes up with 79 posts and about 37 different threads referring to this since 2004. So right at every 2 months.
Slate is also metamorphic, originally from shale which is a sedimentary rock made from clay. Schist is more of a structure of metamorphic rock that is highly layered rather than an actual composition.
My brazilian puffer only puffed up once. He was in my hand out of the water after I squeezed him out of the hose end of the gravel vac he'd gotten himself sucked up when I wasn't looking.
He was fine. Blew some bubbles and floated around drunkenly for a while after I put him back in the water.
The water will also absorb CO2 directly from the air. Airating with a filter or airstone will add CO2 to the water if it's being absorbed enough by plants to drop it below equilibrium with the air.
I found rubber banding some filter wool around the filter intake and then rinsing it out when it clogged up(every 3-4 hours) cleaned up a tank that you could only see 2-3" into in about a day or so.