Dechlorinator removes chlorine, which isn't even a problem in saltwater systems. The major problems in tap water art trace contaminants like dry cleaning fluid, arsenic, nitrates, etc. You also typically have phosphates that will have you back here in a month complaining about hair algae taking over your tank, and silicates, which will cause unsightly diatom blooms. RODI will remove all of that. If $ is an issue, I would opt for a RODI device, and put off the skimmer until you absolutely need it (which might be never). Airwaterice is a web site that sells RODI systems. I have had mine for at least 10 years without a problem. They are very knowledgeable, and will give you good advice over the phone.