I have decided to purchase an RO System because my Tap Water Source reads: Ammonia: 0.25 ppm Nitrite: 0 ppm Nitrate: 10-20 ppm pH: 8.0-8.4 kH/gH: 12-14 My fish have recently been dying. Mollies have been dying. One of the easiest fish to care for. They are mainly juvenile-adults that are healthy, no fish are sick, they are fed well, yet I have been losing many recently. I believe it has to do with the 8.4 pH in the aquarium and the 0.25 ppm Ammonia. I do weekly water changes but even then, the new water I am adding has Ammonia, and a high pH so it doesnt help the water parameters. I have been looking into RO Systems and there are several different ones, such as 3-Stages, 4-Stages, and 5-Stages. But which one should I buy, I will be using it in a 30 gallon tank as I have nowhere else to store water (as in space) I have two tanks, 50g with fish, 30g running with no fish. That is the only place i can set up the RO System. So can someone please help me out with which RO System I should buy? I will be using an RO Additive to make sure the water is safe for the fish and i will slowly switch to RO Water. Thank you.