As Scott pointed out, it looks like your reflections are currently not reflecting anything from above.
Instead of the bleak blue sky, maybe opt for one of the preset physical sky settings. I'm partial to Friendly Afternoon. Make sure to tick 'Use ARCHICAD Sun Position' to keep your own sun direction etc settings.
In detailed settings go to 'Environment > Physical Sky > Compositing' and make sure Sky Reflection is ticked.
Also check at the bottom for 'Options > General Options', make sure Reflection is ticked and set Ray Treshold to 0 so all reflections are calculated.
So after a bit of fiddling about I discovered that increasing the "Reflection Depth" from 4 to 12 in the Options bit of the Detailed Settings made the Black bits go away.
As for the Sky and Context I will be using some images from actual photos of the real thing however I will stick with the "Bleak Blue Sky" as whenever I've been in Barcelona to see the Pavilion that is what the sky looked like
There are other things to fix mostly the surface texture for the Pebbles in the Pond and the settings reflectance and bump map settings for the Travertine, fun fun fun
If you download the free Twin Motion renderer and the ARCHICAD export/sync add-on - you can have real-time preview of extremely realistic (and animated) water, making it faster to generate the scene as you would like to see it.
One of the forum moderators • AC 26 USA and earlier • MacOS 11.6.8, iMac Pro