Purchasing a RODI unit is a great investment. It will help control phosphates, algae, and unwanted elements in your tank. I think whatever manufacturer you choose you will be happy with. I decided on a Spectrapure mostly because of cost and ease/availability of replacing filters. I recommend purchasing the highest output while still fitting in your budget. A 90 GPD unit creates 5 gallons in just under 60 min. If you have a dedicated sink or mess room you might be just as happy with a lower output unit.
You will want to buy a filter that has a TDS meter built in or buy a separate meter. I believe a TDS meter costs about 12$. It will let you know when its time to replace filters and the effectiveness of your filter.
Optimum water pressure for a RODI unit is 80psi. Water pressure does not need to be at 80 psi but operating under low water pressure will take longer to make filtered water, it will create more waste water, and shorten the life of your membrane. Making weekly water for top offs and water changes for a 30 gallon tank your filters (under optimum settings) should last close to two years. Some units come with a booster pump to raise your PSI or you can purchase a separate pump later should you decide it is needed.
