Marine filtration
 

Anyone know if brackish aquarium water requires a special filter or will fresh water filters work good? The reason I ask is that I have a small red clawed crab that isn't looking too good in the freshwater and i have considered getting him a small tank to monitor salt levels in, so is there a difference in the filters or not?

I used a standard power filter on my big saltwater aquarium and kept all kinds of critters in it with no problems.

Use google much?
I don't think it would hurt for a short period of time. If you want to be serious about it though you might as well get the right stuff.

Filters and Filtration

Filtration in a SW aquarium is a bit more involved than that in FW. Since biological filtration is the backbone of a SW system, filter selection is undoubtedly THE most important part of the SW set up process. In all likelihood the filter equipment you are presently using will need to be replaced. The small hang-on-tank biowheel and box, or in-tank corner type filters commonly used in FW tanks are usually inefficient in SW tanks. The traditional undergravel filter (UGF) set ups, although still used by many SW aquarists, contribute to unwanted nitrate problems as the tank matures, and they have lost their popularity as more advanced filtration systems like wet-dry trickle and canister type filters with bio-media chambers have been developed.
As far as what type of filter and filtration method to use, there are no set rules. Every aquarist has an opinion as to which set up is best, but the easiest way to figure out what you may need for your SW tank change over is to decide on whether you want a fish-only or a reef tank system, research the various filtration methods and filter set ups one has to choose from, and then pick one based on what "you" want to try. However, something to consider here is that even if you are starting out with a fish-only tank, it doesn't hurt to begin with a filter set up that can be used for a reef tank. By doing so, in the future if you decide you want to progress into this type of system, you can save some money by not having to invest in a whole new set up.
-- More About Choosing a Filtration System

http://saltaquarium.about.com/cs/bco...a/aa091201.htm

well i don't want to go blowing a bunch of money into it now, i saw some filters that were either mechanical or chemical that were reasonably priced, but for the money i'd rather attach them to a tank worth attaching them to, like 20+ gallons. Currently my freshwater tank is 20 gallons and i picked up a crab while i was out getting some more gouramis, if worse comes to worse i'll let the crab do his bit in life then later put forth the effort for a marine aquarium.