That's prob the best bet but I'm not sure they do tropical. Think it's pond stuff mainly. I used to go to viscum water gardens. Last time I went was when Markham Grange garden centre was open.
Yes They are mainly cold water but they do some tropical fish and the gubbins that goes with them.
The fish folk at Markham have gone after a revamp of the site ( in my opinion not a good revamp)