I tend to use the pet shop in Sydenham. I can only speak for how they treat their fish and tanks, but they seem a lot more organised and look after the fish much better than that HOP shop.

Have been going to the Sydenham shop for a few years now, and the staff (can't remember the name at the moment, but it's on the corner opposite the entrance to Co-Op) are always friendly and seem to know their stuff, most of the animals (fish, birds, mice/rabbits other small animals) kept there are in adequate cages (for a pet shop - yes of course they should not stay there for long, ideally) and unlike the HOP shop, the do not keep larger animals, ie the HOP shop had several kittens in a crammed little cage at the back of the shop for everyone to see. I'm sorry, but I was quite appalled when I noticed that.

As an alternative for a large shopping trip, there's a very large Pets at Home store in Deptford, would that help?