Originally Posted by PiscesLou
but do the fish stay in or out the tank, if in how long can they survive without the filter running?
The fish can remain in the tank depending on how you remove the substrate. The least messy would be a 1-1Â½" diameter hose and syphon it out. That will take the detritus accumulation with it and prevent fouling of the water and filters. Keep the filtration and powerheads running during the removal process but turn off everything moving water when the sand goes in. If you use a plastic cup and lower the sand into the water to the bottom and gentley release it there will be much less clouding. The whole process shouldn't take much more than an hour or so on a 55 gal
tank. Just be sure you have plenty of well aged SW
at hand to replace what you remove.
Once the sand is in turn everything back on. There may be a little dust up but don't worry about it. Even if the tank becomes so clouded you can't see through it the fish will survive just fine. Be sure that if using any mechanical filtration, foam pads and carbons are rinsed out every few hours so the flow isn't affected.