Sand doesn't go "bad", so far as I know, however, sandbeds can encounter serious problems if not properly set up and maintained... You really should read this article, though:
http://www.rshimek.com/reef/sediment.htm
It will dispell many of the "myths" that are out there about sand and sandbeds, as well as give you some more information you can be armed with against greedy LFS's looking to sell more to the uninformed.
If the sandbed hasn't been set up for very long, which it doesn't sound like it has, and hasn't had a heavy bioload to pollute it, there isn't any reason I can think of as to why it would need replacing. I'd have the school keep the sand they have. Maybe just stir it up a bit and add some activator kits to it. There are many to be found online, and it'd be cheaper than getting a whole new bed for a tank that size!!! Try http://www.ipsf.com/ or http://www.garf.org/aragwk/aragareadyorder.html (scroll down until you get to the sand activator part), or search around for others. You can even get about 300 ml of sand from your own established tank, along with the same amount from whoever else you know in the area with a marine tank, and dump that in to "seed" the tank. Thats free, too.
As far as the water... That's where I'm more of a stickler. Certainly, replacing all of it would be a major feat and would expose much of the rock/tank to air, killing off a lot of beneficial bacteria. I'd replace it gradually over a week or two, and as long as the water is keep moving and evenly heated, should be fine. I would not, however, under any circumstances, ever use tap water. RO/DI is the way to go. For a tank that large, it isn't cost efficient to get it from a LFS or water shop; see about having the school buy a unit specially for the tank (shouldn't run more than $150-300.00, typically), and make the water from that. Will save a lot of $$$ over the long run. You'll have to do your homework on RO/DI units and the whole maintenance process.
Hope that helps, and good luck!
I'm thinking of eventually getting a tank that size, but I'm moving cross country in the next 6-7 months, so that won't be for a few years, until I'm more established...
http://www.rshimek.com/reef/sediment.htm
It will dispell many of the "myths" that are out there about sand and sandbeds, as well as give you some more information you can be armed with against greedy LFS's looking to sell more to the uninformed.
If the sandbed hasn't been set up for very long, which it doesn't sound like it has, and hasn't had a heavy bioload to pollute it, there isn't any reason I can think of as to why it would need replacing. I'd have the school keep the sand they have. Maybe just stir it up a bit and add some activator kits to it. There are many to be found online, and it'd be cheaper than getting a whole new bed for a tank that size!!! Try http://www.ipsf.com/ or http://www.garf.org/aragwk/aragareadyorder.html (scroll down until you get to the sand activator part), or search around for others. You can even get about 300 ml of sand from your own established tank, along with the same amount from whoever else you know in the area with a marine tank, and dump that in to "seed" the tank. Thats free, too.
As far as the water... That's where I'm more of a stickler. Certainly, replacing all of it would be a major feat and would expose much of the rock/tank to air, killing off a lot of beneficial bacteria. I'd replace it gradually over a week or two, and as long as the water is keep moving and evenly heated, should be fine. I would not, however, under any circumstances, ever use tap water. RO/DI is the way to go. For a tank that large, it isn't cost efficient to get it from a LFS or water shop; see about having the school buy a unit specially for the tank (shouldn't run more than $150-300.00, typically), and make the water from that. Will save a lot of $$$ over the long run. You'll have to do your homework on RO/DI units and the whole maintenance process.
Hope that helps, and good luck!
I'm thinking of eventually getting a tank that size, but I'm moving cross country in the next 6-7 months, so that won't be for a few years, until I'm more established...
