[DutchmenSport]

So the question STILL remains, where did the water go?

My thoughts? Although it came out of the tank somewhere, it's flowed onto the underbelly Coloplast and then dripped on out to the ground. This is assuming hundreds of gallons of water went somewhere.

Where did it leak out of the tank? Considering you added back another 10 gallons, and experienced no more leaks, I would expect to find a crack at the top of the tank, or at the joint where it connects to the toilet pipe.

Fill your tank to the brim again. In other words, fill it until water actually comes up in the neck of the toilet and then check if water is spilling out out somewhere.

I'm assuming you already removed the Coloplast?