Most Dual Chamber CA reactors just provide a place to put extra CA media so that you don't have to fool with it as often. The pH difference between the 2 chambers is only sightly different. It would be a better idea to aerate the effluent from the reactor in a cup or holding area rather than having it go straight in to your tank or sump if you think that's where your pH problem is coming from. That would be more effective at raising the pH of the effluent from your CA reactor than adding just a second chamber IMO.

You could also just give it a try and tell us what happens since I don't think that you'll be putting any media in the little fishes reactor. Who knows, you might have a great little experiment in your hands.

-David