Personally I have always said if you mess with the sand you will have problems. In the past when I have needed or wanted to change the substrate on a tank I followed the following format and have never had a bad result from doing this, other than never being able to stack back the rock the exact way I had it before. IMO this is the best way to do this. It is pretty much just like changing out tanks. I copied this over from another post I wrote so it was written for a different size tank. For a 40 gal you will need only 5 ice chests and 10 gals of replacement salt water as well as 5 -8 gals of rinsing saltwater. Just be sure to wash and drain that new dry sand before starting the project. Hope this helps and
Merry Skerry
1. Turn off all equipment and fill one ice chest full of new saltwater.
2. Pump water out of tank into remaining ice chest being careful not to disturb the bottom of the tank and substrate. You want only clear water. Leave enough room in each chest to place part of your rock in.
3. When pumped down to about two inches above substrate stop and remove all coral and rockwork to waiting ice chests full of your clear water.
4. But before placing in clear tank water give them each a swish in the new saltwater for a moment to remove loose deteris. This will be discarded and not reused.
5. Now that all rock work and corals are removed it is easy to catch all livestock and place them in chests w/ the rock and corals.
6.. Now finish pumping out water into waste buckets and discard. Remove crushed coral by scooping out and discard. Use a wet vac to remove remaining water and substrate.
7. Now is a good time to do a little cleaning on the inside of display if needed, by wiping down ect...
8. Now place in your new aragonite dry sand substrate. (2" or less)
9. Replace your rock and corals
10. Fill with reserved tank water
11. Replace livestock to display when water is 1/2 full.
12 Replace lost water volume w/ new made up saltwater. Normally about 20%
13. Turn on all equipment and insure all is operating properly.
14. Suppliment w/ a little live bacteria to replace the 10% loss in nitrifying and denitifying bacteria.
It takes two or three people to do it and a little planning, but the whole thing takes about 1.5 hours to complete from start to finish.
