Where does the reactor go?

So I am in the process of designing a sump for a 75-90g aquarium (havent decided yet), and I can't figure out how phosphate reactors work. I come from hang on the back filters, which already have carbon media in them, so I am a bit confused as to how I need to lay this out.

First off, are they necessary for a reef tank, or can they be added later?

Second, does it just get plugged in between the overflow and the sump? Does it need a pump, or will it siphon itself through?

Lastly, how much would a value system run? I don't know whether I need the full RO/DI system or what. Any recommendations?


Thanks!

 

They are not necessary, but are good to have will help keep your phosphates down and yes can be added later down the road. Second it can be placed inside your sump or placed outside your sump it's all up to you. You will need a pump for it and lastly they depending on what one you will get will run around $40 - $45 dollars