I have been using my ro system without the membrane for my auto drip system on my ray tank. I'm setting up a saltwater tank and want to remove the ro system to use for the saltwater tank. I want to buy a new water filter but am unsure of what to get. I want to get one of the following http://www.h2osplashwaterfilters.com/unwafi.html I'm not sure if one, two, or three filters are needed.