My vote is a MRC dual reactor. Arm Standard Media. Aquarium Plants Electronic Carbon Doser Regulator. Continuous duty peristaltic pump to feed the reactor.
There is lots of different methods listed in this thread and also some misinformation.
You are adding CO2 to your tank, it will effect your PH by lowering it, not raising it or keeping it stable.
The reactor is a plastic tube, it really doesn't matter as long as it holds water, media, and has a pump that circulates the water. Brand whatever. Some suck, some are mediocre, some are excellent. As long as it cannot build up CO2 inside the reactor by being trapped then it will work.
Feeding the reactor with a normal pump and using a needle valve to regulate water through the reactor is IMO the cheap way out. It may work for most or for some but I personally don't like to fiddle.
I have worked with many reactors over the years and solved many peoples problems. I will not stray from the setup I listed above and you couldn't pay me to. I would not run a reactor without a continuous duty peristaltic feed pump, I would just assume dose 2 part.
You absolutely do not need a controller to operate the reactor unless your reactor is unstable and will not function without one.
This is two screenshots from my controller sat side by side so you can see my reactors ph stability. 3.5 months and it has changed by .04 ph. That is without any control, just the reactor running happily ever after... You will not find a more stable system then what I am recommending and you will not find a single person who has followed that setup who regretted it. Be warned, there is some sticker shock involved. If you want to venture into this setup I will help you from beginning to end to make sure you get it right.
The reason I am so confident in this setup is because ph probes wander, sponges clog, feed rates change, and media dissolves. All of these effect the outcome but none of them will effect this setup.