Calcium reactor suggestion?
 

I am planning a 90g reef tank (mostly zoos with some LPS), will a calcium reactor help keep cal/alk in check?

What is a recommended brand? It has to be external as my sump won't be big enough for more than a pump (considering the room the skimmer, return pump, heaters, GFO pump, and small refugium take up).

Any assistance is appreciated.

I love my GEO. Built like a rock and easy to use and set up.

Take a look at dosing systems like Profilux or some of the cheaper brands. Calcium reactors are starting to become "old school" with dosing systems taking over. They take up less space, a bit cheaper to setup, and more flexible.

Been using a precision marine RfCA6 and it keeps my calcium levels spot-on with minimal work needed from me.

Platform shoes were once in fashion as well :D

Both two-part dosing and calcium reactors have their pros and cons. One must weigh all factors in deciding which one to proceed with. As with everything in this hobby there is much research to do. Financially speaking, I believe that Randy Holmes-Farley did a comparison between dosing with bulk chemicals and a calcium reactor and found that dosing was cheaper up until around the 100 gallon point above which reactors became more economical.

I've done both and found that I like the "set and forget" nature of a reactor to be the tipping factor.