27 gallon reef tank

+1 to astrick117 -- you will need all of what he mentioned, you can probably do without a RO/DI unit as they can become expensive.. I pay 1.99 for 5 gal at my local organic grocery store.

When purchasing salt, try to find one specialized for Corals and not just Saltwater aquariums. They both contain the same minerals necessary, just the reef salt would probably consist of high levels of concentration per mineral, example would be Ca (calcium) I think the stuff I bought for salt tanks was around 380ppm Ca and the new salt I purchased specific for reef tanks is around 440ppm Ca which is much closer to the ideal level of 450-460ppm Ca

Also I wouldnt bother with any elaborate or expensive test kits.

Get your basics for Ammonia, Nitrates, Nitrite, also Phosphate and Calcium, along with pH and kH. Realistically any good reef store should be willing to do free water testing and go over the results in detail if they are friendly enough.

 

I got a refurbished RO/DI from SpectraPure for $120 cause the closest place for me to get RO/DI water is about 30 min and it is $1 per gallon. The other benefit is that you know the quality of your water and you will be able to change the filter when it is needed.

If you can get a deal like 5g for $1.99, that is pretty good and you may want to go that route instead. I just know it has paid off for me.