I think it's the best $65 you can spend. Have you seen this unit?
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I use the same one myself for all my tanks. It's portable so you can either hook it up to your faucet or garden hose and then put it away. It gives me 0 ppm of tds in my water, no nitrates or phosphates. And best of all, no more lugging buckets to the store! LOL
It is a smaller unit so the filters are only good for so long, but I got 6 months of use out of the first set of filters and the replacements were $28. BUT I make far more water than you will so it should last much longer.
Before I got the ro/di unit I was lugging water from the Publix supermarket from their ro/di machine. It was checked weekly and had a dual stage di on it so I felt good about using it. It cost 30 cents a gallon but it was a pain to go every week.