Awesome, How long did you need to wash it for and did it settle alright in the end?
I used the little hose thing from the detachable shower head in my bathroom, a big 12L bucket and 1/2 - 3/4 of the sand each time. Took maybe ten minutes of swishing the sand around, letting it overflow, waiting until the water cleared, e.c.t for each lot of sand that I did. Might need two or three buckets depending on how much sand you're using. I used hot/warm water straight from the tap to wash it. It was cold that day so I didn't want to wash it outdoors.
I got two 15kg bags for £10 from Argos.
Sorry if this is hard to make sense of.
Basically, ten minutes or so of washing each load of sand, and then left it in the bucket(s) overnight. It settled very well with about an hour or two of cloudiness and then absolutely nothing.
I put the fish back in once the water was up to temperature, since my filter was already established and would be able to cope with the complete water change.
No deaths, even all the snails and tetras survived. No stress, their colour returned to full brightness after about twenty minutes.
This thread from a few weeks ago was where I learned a
lot about sand and switching substrate. Then I made
this post in my journal briefly covering how I went about doing it.
Again, it's a bit troublesome but it's very rewarding.