I went there and got some fairly decent shots handheld. Basically high ISO is what you need. Most of the fish tanks are quite well lit. The biggest problem is the dirt on the tanks, and the quality of the glass.
Isn't it closed for a complete refurb? Or is that not happening yet?
Looks like the refurb finishes in March. According to the blurb, some attractions may be closed. Hopefully the worst is done!