Hiya,
On a few tanks when i've renewed the sand all's i do is start a syphon using common garden hose and slowly vacuum the sand out
That said on a few occasions i've left fish in and topped the water up with dechlo included, on other occasions i've cupped/netted the fish out
If the fish are small and likely to get sucked up i'd air on the side of removal, but larger fish i'd leave in
Whatever you do, use fresh sand, wash wash and wash some more or you'll end up looking at a tank of what seems like flour water lol
Ohh and a tip for you ...............
When the tank is ready for new sand, make sure there's more water in than the required depth of substrate (only really applies if fish are out and you run tank totally dry)
Then with fresh nicely washed sand just put about 1 litre of sand in at a time (i use a 1litre plastic food jug) and spread the sand around
Doing this is twofold, one it's easier to spread out, two you won't get trapped air bubbles in the sand layer/s
Hope that helps
Tony
