Premium Aquatics is a good source for reverse osmosis/deionization units. You can order them online at the following site and any of the brands they carry are reliable, well-known brands used by reefkeepers and marine aquarists:
Click here: RO/DI Systems: Premium Aquatics
If you’re looking for a bargain, several hobbyists have found good deals on RO/DI units on eBay, so you might consider researching the brands on Premium Aquatics and then looking for a good price on one of them via eBay.
What ever reverse osmosis unit you decide on, Sandy, it’s a good idea to get a deionization (DI) filter for it as well. It won’t add to the total cost that much and it further improves the purity of the resulting water.
Another option you may want to consider is buying reverse osmosis/deinonized water (RO/DI) for your water changes rather than installing an RO-DI unit of your own. Most well-stocked pet shops that handle marine fish sell RO/DI water as a service for their customers for between 25 and 50 cents a gallon. If your LFS does not, WalMart sell RO/DI water by the gallon for around 60 cents, and you should be able to find a Wal-Mart nearby. Always bear in mind that when the water used for mixing saltwater is RO/DI or another softened source, a commercial buffering agent must be added to it before you perform your water changes in order to prevent pH and alkalinity drops.
Natural seawater is another good option for water changes. Like RO/DI water, natural seawater can be purchased at fish stores for around $1.00 a gallon, depending on where you live. It sounds expensive, but when you consider the alternative — paying for artificial salt mix and RO/DI water and mixing your own saltwater — then natural seawater is not a bad bargain at all. It has unsurpassed water quality and seahorses thrive in it.
The type of chiller you need depends to a large extent on the size of your aquarium, how hot it is running under normal operation, and how much you need to drop the temperature. However, I can tell you that I have heard some good reports from seahorse keepers regarding the following chiller by Current:
Click here: 1/15HP Prime Chiller w/Dual Stage Thermo (Current)
Check out the specs on the above chiller, and if it sounds like a good match for your particular aquarium, Sandy, then you can do a Google search to compare the best prices from different companies that carry that unit online.
These would be good questions to pose at the seahorse and pipefish forum on Reef Central. Delicate corals and invertebrates require optimum water quality, so most reefers use RO-DI filtration for their reef systems. Likewise, traditional reef systems use high-intensity lighting that generates a lot of heat, so many reef keepers use chillers to keep their water temperature in an acceptable range. So before you make a decision on what brands work best for you, I would also run your questions by the folks at Reef Central to see what they would recommend in that regard.
Best wishes with all your fishes, Sandy!