Thanks for that Rob - think I'll try that shop one day soon!
I've just switched my substrate for my small tropical tank from gravel to sand (neon and glowlight tetras, clown loaches, bronze corys, an odd flame tetra - got in the bag with the neons and got it for free! - and an absolutely ancient silvertip tetra. Oh, and a catfish that looks like a twig).
The switch went OK, but after testing the water today I've got a bit of a nitrite spike going on - will have to keep an eye on this.....
When this tank is stable, I'll be looking for more fish for my other (african cichlid) tank.
Tracey