That is a hard question. There is no easy way to do this since if you let the filter stop, all of the bacteria will die off after a few hours and it would be the same as if you had simply removed it.
Can you tell us about any other filtration that you have? Liverock? If you have sufficient filtration, removing the biological filter should pose little problem. You will probably experience some nusience algae for a few weeks until the bacteria balance adjusts to the change. For the first couple of weeks after removing the fluidized bed I would test the water frequently (Daily or every other day) for ammonia and nitrite.
I wouldn't necessarily soak the sand. If you do the I would think several hours would be enough and it doesn't matter whether you use the water from the bottom of the tank or from the top.
You should shoot for 4"-6" for your sand bed depth. Good luck.
I would add the sand using the technique that follows:
<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr> I Added a DSB to my established 55 and can give you some advice. First, it is a pain in the butt! It took me about 5 hours total. Get a bunch (2-3) of rubbermaid containers (32 gal), and mix water like you were going to do a water change. Siphon off enough water to fill to 1/2 the vol of your rubbermaid containers.
Move the LR to the containers as you are siphoning, and place the corals carefully on top of the LR. I did not bother to use powerheads or heaters in my containers; I just worked fast.
When the water level is low in the tank (the lower the better), remove the existing substrate using a scoop. You may want to leave some to seed the new bed. You now may want to use some PVC on the bottom of the tank as a base for the LR so that burrowing fauna doesn't topple your LR.
Now add the sand using the scoop. This keeps the water from clouding too much. Make sure the bed is fairly even, 4-6" deep. Add the LR from one container at a time leaving the corals in the containers for now.
Then place a large tupperware dish in the bottom of your tank as well as a heater. The sand is probably colder than the water which will cause your water temp to drop. Since your sump is not in circulation, the heaters there will not help.
Using a powerhead/pump and a length of tubing, pump the salt water you mixed for the water change into the tank. Coil a small length of the tubing in the tupperware container so the water being pumped up is not being pumped into the sand bed. This will GREATLY reduce the clouding in your tank.
Now pump the water from the containers holding the corals. As the water level in the main tank rises, add the corals one by one.
Once the tank level has risen enough, continue to pump from the containers that held the LR and corals and simultaneously siphon off the foam produced by adding the sand and some of the cloudy water.
Run your skimmer and your powerheads. The storms will persist for less than a day, and in 48 hrs max your water will be crystal clear again.
I did it this way and only lost one cleaner shrimp that I accidentally burried.
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