There is an indoor pool too Gortex. i think its just the fact that it looks better suited to a 3* hotel in spain then a sealion pool but thats just how it was built in the past, not much can be done now.
I think it looks outdated. although it may be fine size wise, there is very little contrast in areas, ie no natural substrates, rocks etc with only a basic concrete floor and a few stands for the sealions. I think that whipsnade should make a totally new are for the sealions (due to the inability to modify the current enclosure to a great enough degree)