Ok im scared now. First marine tank, a very small one, and your making important mistakes before you even get it?
1. Marine bacteria differs completely from freshwater bacteria. The biowheel will die and start again, Id clean it. Same with the gravel. I'd actually lose the biowheel, in a marine tank a biowheel is nitrate factory, a protein skimmer will remove the wastes before they break down.
2. For stability, I'd go with the substrate as aragonite sand. If that costs too much, go with silica sand, does not have the buffering capabilities, but it preferable to gravel.
3. I am not familiar with the eclipse system (its an eclipse on a ten right?), but if you can get a couple oyster shells, crush them, put them in something to hold them together, submersed in the water. That will bring your buffering capacity up to level.
4. Skimmer is a VERY good idea, its only $70, for a prizm, it will fit the tank (you may have to mod your eclipse hood). On marine tanks we like to take out wastes before the bacteria breaks them down, using foam fractioning, which only works on marine.
5. Carbon is another good idea. The skimmer removes the larger wastes, the carbon will take the very small wastes up. Larger time between water changes.
Theres more... I just can't think of it... going to work now... first day working at my LFS
