Which RODI filter do I need?

[Areet Reef]

This is my first marine aquarium after years of keeping planted freshwater tanks. I've bought the Waterbox Marine X 90.3.
My tap water has a Total Hardness of 120, this is from a test strip.

What RODI system do i need?

4 stage seems to be the most popular but do i need 50/75 or 100GPD?
Thanks in advance

 

[Rennurdoar]

I'd go for the 75/100GPD for that tank. I have a 75GPD that I use for our 90gallon. (And used previously for our 65gallon)

Just have to pick which brand and one you like the best

 

[Rennurdoar]

Also, do you know what your Tap water TDS is? That would help determine whether or not you get a 4 or 5+ stage as well.

 

[Opus]

GPD is up to you. It is best to know if your water has chlorine or chloramines. If it has chloramines I would go with a 5 stage with 2 carbon blocks to make sure it takes out all the chloramines. Down the road you can add stages if you fill the need. Some people go with more than one DI canister or break out the DI. Also invest in a tds handheld. If you are having issues with the unit, the first question asked will be what is your tds at various stages of the RODI process.