I purchased an R.O. unit off of E-bay. It was $99.00 for a 6 stage R.O./D.I unit with a 4 gallon tanks and faucet connection. Makes 125 GPD if necessary. Works great and if you have never tasted R.O. water, you don't know what you are missing.

Our water here is 33deg GH and over 20 Kh. If I let water sit in a glass for 3 hrs, I can see the sediment in the bottom of the glass.
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Member of the AGA (Aquatic Gardner's Association)
Member of the IBC (International Betta Congress)