I tried the water softener pillow from kent Marine I think, in my 55 gallon tank. It was not rated for a tank that large but it did drop the hardness a little. After that I just got RO/DI water. It was only 30 cents/gallon at the LFS and the water softener pillows were 12 or so (rechargeable with solution that you have to buy). For the money I would say to go with RO/DI as that is what I would do now. I don't know how hard your water is or how big your main tank is, but I think they like pretty soft water. I would change maybe as much as half depending on the size of the tank to lower the hardness by half.