Well after much putting it off. I finally took the plunge. The white gravel I had in there was starting to look disgusting, and my other half agreed that changing it was the way to go.
The whole process took about an hour, and was relatively straight forward, we kept the fish in a bucket, with the filter running while we did the work, but they seemed ok!
The most difficult part was, even after taking out all the ornaments and draining the tank to around 1/4 full, the fish were still a right bugger to catch! Especially the Rummy Noses, they are very fast!
Just got some normal beach coloured sand, when first putting it in, it looked like a dark brown sloppy mess, and I'd wondered what I'd done, but after the water de-clouded (which took about 5 hours) and I put the lights on it all looks beautiful now!
My concern now is how to keep it clean when it inevitably gets dirty again, I'd imagine it's very easy to suck up most of the sand while trying to clean the poop off it!
I'm going to leave things for a couple of weeks to let them settle down, then get a couple of Cory catfish.