RO/DI filter help

[Jcm412]

Sorry if this is a basic question. What type of RO/DI filter do I need? 4 stage, 5 stage, 6 stage? What is the difference? Do I need to get my tap water tested to decide?

 

[Big G]

Check out this video from BRS. It's from their 52 weeks of Reefing series:

https://www.bulkreefsupply.com/video/view/week-7-how-to-produce-the-best-water-possible/