[mike31154]

The system you have with the pressure tank is primarily designed to conveniently provide relatively pure drinking water. This is accomplished through the pressurized tank and a dedicated faucet to dispense the water. Great little set up for your nano but if you're going bigger, you're better off using a larger, open, non pressurized container as illustrated by sphelps. A larger pressure tank would certainly work on your current set up, but you're still going to need a large container to mix your salt water.

In addition, depending on the quality of your tap water and the livestock you intend to keep in your new, large system, you may need to add a DI stage to the system to bring the TDS of the water you use down to 0. If you don't have a TDS meter on your current system, or a handheld TDS meter, it will be a good investment before you go buying more add ons for your RO system.

A final thought, with your current system you're pretty well limited to the 'Kenmore' filter cartridges. I think most of us in the hobby get RODI systems which use the more standard 10 inch filter housings which allow you to purchase more generic and less costly filters/pre-filters.