...at least it has natural sunlight?
Not sure if there are any seals in the pic so that I could gauge the size...
(Seriously, that dark paint coating the pool and constantly looking at that must be depressing for the seals!)
There are two seals in the pic and I think four in the actual exhibit.
It is not large, but for an indoor pinniped pool in Asia it's doing okay.
On your last point, overall light levels may or may not be an issue, but surely a dark coating on the pool itself is more natural and better for their eyes?