Most fishtanks have to stay in a pretty narrow range of temperatures or the fish die. A big professional installation like this I expect will have both water heating and water cooling (aircon, but for water).

And in a glass fishtank, the glass is in good thermal contact with the water, but bad thermal contact with the room air - so the glass will end up being at fishtank temperature.

So, unless they had extracted all the fish and turned the tank heating off, I don't think what you say is true.

That is one eventual first quick assumption by some (mostly nontechnical journalists), but nothing official and confirmed, or you have sources? Otherwise please don't sell this as fact. Knowing the place, it still had heating, so I personally find this also unreasonable.. would only make sense to me if it got to freezing temperatures or below 4°C, but that for sure wasn't the case.. I doubt that place was much colder than at other times, like maybe 2-4 degrees.. but if you have any real details on that this would be welcome.

It's filled with tropical fish, so surely the water would have been at a decent temperature - definitely nowhere near freezing. The thing was in a fancy hotel lobby too (I was there once for an Apple event), I doubt they'd let the place go down to such low temperatures.

And you do have first hand information, that this was the reason, as you speak with such authority of that matter?

Like, you do know that the temperature in that hotel was significantly lower than last year?

I mean, it seems possible, that it was the reason, (even though the water temperature itself hopefully did not change as the fishs do not like that) and the last nights were quite cold in germany, so stress from temperature difference is possible, but before I claim to know something, I wait until I know.

There was first cold weather recently as well. November was VERY mild.