If you want to completely remove the sand bed and then replace it this is what I would do.
>drain the tank about half way, then put that water into a temp bucket and put your livestock in their. Add a heater and a power head for water movement. then drain the balance of the tank into other buckets. Now just take a shop vac and suck it out and clean the bottom. Then add your new sand and put the water back in. It will be a dust storm so you would want to keep the live stock out for the night, then test it the next day and add the livestock back if its good
>If you want to just add the sand on top, one way I have done it is to get a 1 1/2 peice of PVC pipe and the put one end on the bed and start slowly pouring the sand in the other while moving the pipe over the bed to spread out the sand evenly. I would suggest only doing about a 1/2 inch at a time, then wait a few days and do it again. This way it should stress out the critters to much
Hope it helps
Mojo