Yes,
RO means reverse osmosis. The water has been passed through a membrane and maybe carbon to remove the chlorine and a lot of the dissolved solids that make the water hard. There's a description of each stage of the
RO process on the side of the machine that I get the water from. Actually, the
RO machine that I use has an Indianapolis address on it!
This machine is about as big as a pop machine and it's in our grocery store. You can buy a jug there and fill it, or bring your own jug and fill it, usually for a reduced price. I think the price per gallon is 39 cents if you bring your own jug. This works out fine for my 5 gallon betta tanks. A lot of people with
SW tanks have an
RO system in their house.
Maybe some
lfs in your area have the
RO water available too. The hatchery that I go to has a big
RO system and I got some from them when the grocery store machine was down for a few weeks.
The filter that I was talking about in my 2.5 gallon
QT tank is a Whisper internal filter. I don't like this filter, actually. It just keeps the water moving a little bit in
QT to keep the temperature stable or keep the medicated water circulating. It doesn't do much for the cycle. You can't really put any media in it, besides a bag of carbon, which you wouldn't use with medicine anyway.
The filters in my 5 gallon betta tanks are sponge filters. Here is a link to what I have:
http://www.drsfostersmith.com/Product/Prod_Display.cfm?pcatid=3954&inm=1&N=2004+113425+113565
The same airpump runs both filters: (the smallest pump)
http://www.drsfostersmith.com/product/prod_display.cfm?pcatid=3676&N=2004+113590
and the airflow coming out of the pump is adjusted by a gang valve.
http://www.drsfostersmith.com/product/Prod_Display.cfm?pcatid=3700&inm=1&N=2004+113404+113565
I have a 3-way gang valve -- one port for each tank and one port that I open up to let off excess air. All 3 ports are adjustable. There is a picture and a description of the gang valve-airpump setup in my gallery. The gang valve that I linked to show you isn't the exact one that I have, though.