Dual chambered calcium reactors are advantageous because unlike a single chambered reactor, dual chamber reactors have a higher effluent pH which allows it to maintain the same calcium and alkalinity output. This helps to prevent a low Ph value in your tank.
Reverse flow reactors are nice, too, because they allow for more contact time with the reactor media. I think once you figure out what type of reactor would suit you best you'll able to narrow it down to a specific make/model.
Well, single chambered reactors are just fine. I was only pointing out the advantage of a stable Ph value that the dual chambered reactors offer. After all, I am using a single stage reactor myself - Korallin 3002 - simply because it's more cost efficient for me (I live in So. Cal.) But I do have a huge dual chambered reactor - Marine Life Aquatics CR-1500 - that is sitting unused in my garage because of the Iwaki 40 it utilizes for re-circulation. It's just not cost effective for me to use because of that pump.
Have always liked H & S products, how is your doing? Holding a constant calcium level and if so what is it. I'm having problems with my Korallin. Pls let me know, am interested in finding a stable, reliable reactor and have used GEO as well