Actual testing of the Horizontal Reactor
My supposedly accurate
Hanna CO2 test kit is on backorder, so the most accurate way I have to measure my CO2 injection rate is through pH readings and the
pH drop method.
Read @Dennis Wong 's excellent article on measuring pH drop here. I also use glass drop checkers just to double check my findings.
Dissolved CO2 gas has a direct effect on lowering pH in our aquariums. There is also some relation with kH (a reading of carbonate hardness in your water). For most tanks between ~2-6kH, a 1.0pH drop equals about 30ppm CO2, which is high and ideal for growing plants, and my target for CO2 injection. I have extremely low KH tanks (between 0 and 1, I can't actually test it with the API test kits it's so dilute). With KH this low, you might need a 1.4 or 1.5 pH drop
The "Drop" is the difference measured between your CO2-injected tank water, and from a sample of your tank water that has been completely de-gassed of all dissolved CO2. You can degas a sample by leaving it out open-top on your counter for 24-48 hours, or through aggressive agitation (blending, stir plate, vigorous shaking).
Steps I took:
- Set up reactor at about 2/3 full H2O to start (rotated until top of outlet was about 2/3 height of the inner reactor).
- Took a sample of my aquarium water and put it on my stir plate with a stir bar for about 20 minutes, aggressively de-gassing my sample.
- Calibrated my GHL Profilux aquarium computer and pH probe with ph4 and ph7 calibration fluids.
- Measured the pH of my degassed sample after 30 minutes of stirring, then set up the probe in the aquarium.
Results:
The degassed sample reads about 6.8pH. I'm pretty skeptical of this, since this tank is FILLED with ADA Amazonia and driftwood. However, the probe reads the calibration fluids accurately, so I wonder if it has to do with my low KH and low GH? KH is <1, and GH is about 4-5 (100-130 ppm TDS). I'd expect a tank like this to be much lower, about 6.5, but I could be wrong? Either way...
The CO2 turns on at 7:30am and off at 4pm. Here are the first day's results:

Note that the tank had CO2 injection from the previous day still degassing. It would take days for a tank of this size, even with my very good surface agitation, to completely degas. With a very low KH, I think it's normal to have a ~1.0pH drop already before injection happens the next day (at least I hope!).
It took about 3 hours to reach my target 1.5ph drop (from degassed to injected). This isn't too bad with a tank of this size, but I was expecting better results. I also re-checked my degassed sample, both quickly with another 30 minute stir plate session AND I left my pH probe in the degassed sample for 11 hours all night, just to check. Yep, it's about
6.8ph (and clear that even 30 minutes of aggressive near-blending stirring is
still not enough to fully degas your samples. You better shake them hard!). The lowest it dropped was about a 1.6pH drop, which should be plenty for my tank. Drop checkers were lime green at that point.
Day 2 showed similar results, 3 hours to a 1.5pH drop and a whopping 1.7pH drop at the 8 hour mark. Good, but I still want to reach that bottom level faster if possible just to see what it's capable of (the tank is only just planted, and I have no livestock inside). Let's increase the rate of CO2 by rotating the reactor to maximum strength (1/2 filled):

Now we're talking! The reactor reached a measured 1.5pH drop in only 2 hours on this huge tank, with tons of surface agitation. That's great!
But holy shit, a 1.75pH drop in 6 hours? That's absolutely going to kill my fish. So, while the curve got steeper quicker (and you can see that it really was able to bottom out much faster) it's going to likely be too much for my future inhabitants (drop checkers were slightly yellow at this point). I'm very curious to see what the Hanna test kit says about the ppm CO2 concentration here. Let's repeat another day:

Great results again, a steep curve that bottoms out at about a 1.7pH drop in 6 hours, with a ~1.5pH drop in 2 hours again.
My thoughts so far:
NO SPRITE WATER!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! I could scream my praises all day long. All you suckers saying "I don't mind the CO2 bubbles" have CLEARLY never seen crystal clear water through low-iron glass, where the only bubbles are from the plants pearling (I'm just joking, no one is a loser here). But seriously, having a method of CO2 injection that is this silent (it's VERY silent), doesn't impede my filter's flow, doesn't need cleaning like in-line diffusers, has a built-in safety in the overflow concept, is easily adjustable by simply rotating the reactor around slightly, AND keeps my water completely clear of CO2 bubbles is an absolute win. I genuinely think that many (if not most) of the world's future aquascaping galleries (Green Aqua, ADA, Liquid Nature, ADG, etc.) will be running horizontal reactors on their tanks.
It's annoying that the acrylic reactor from ARC has the super large 6" flanges on the sides, whereas the stainless steel reactor doesn't... but you can't see inside of it to quickly diagnose if something is wrong.
I think I'll likely end up setting my reactor to about 2/3rds full of water, and just starting it a few hours earlier, so the bulk of the peak of CO2 injection falls across the tank's photoperiod.
Please feel free to ask questions, request pictures, poke holes in my reasoning, or any other comments!
And here's a sneak peek of the tank-to-come:
