Finally getting my CO₂ curve where I want it on my UNS 60U

[TheBurn]

I recently added a small adjustable powerhead/wavemaker that's set to constant flow mode to increase surface agitation, gas exchange, and overall circulation. The goal wasn't to reduce CO₂, but to use stronger gas exchange along with adequate injection to get CO₂ up quickly before lights-on and then reach a stable equilibrium instead of continuing to accumulate throughout the photoperiod

Big thanks to @Dennis Wong / 2Hr Aquarist for his articles explaining this approach. I've learned so much from them. It's completely changed how I look at CO₂ injection and surface agitation

For testing I'm using a freshly calibrated Apera PH60 for pH, Hanna Checktemp 1 for temperature, and the Hanna HI3818 CO₂ titration kit to check actual CO₂ concentration. CO₂ kicked on at 12 PM, lights came on at 3 PM, and CO₂ shut off at 8 PM

Tank/water parameters: UNS 60U, Controsoil, RO/DI remineralized with APT Sky, GH 5 to 6, KH 0. My best degassed pH reference is around 7.30, so I'm seeing roughly a 1.7 pH drop at plateau. With 0 KH the standard pH/KH chart doesn't apply, so I'm using the Hanna kit alongside pH to track the curve

Today's testing showed a really good trend. The tank was already at pH 5.60 by 2:30 PM, reached 5.59 at lights-on, and stayed essentially flat through 8 PM. Hanna measured approximately 44 ppm at lights-on and 44 to 45 ppm at the end of the injection period. Since I was essentially at plateau 30 minutes before lights-on, I now feel comfortable reducing my pre-light injection from 3 hours to 2½ hours and seeing if I can still reach the same level by lights-on

My original CO₂ target was around 40 ppm, but at this point I'm wondering if it's worth trying to make a microscopic needle-valve adjustment just to knock off ~4 ppm when the curve is this stable

Would you guys leave it around 44 ppm or bring it down slightly closer to 40?

There's no livestock yet, so I'm taking advantage of this time to get everything dialed in. Plants are doing great. Planned livestock is cardinal tetras, pygmy cories, Amano shrimp, and eventually Caridina, and I'm planning to start stoc
king next week

 

[Naturescapes_Rocco]

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I recently added a small adjustable powerhead/wavemaker that's set to constant flow mode to increase surface agitation, gas exchange, and overall circulation. The goal wasn't to reduce CO₂, but to use stronger gas exchange along with adequate injection to get CO₂ up quickly before lights-on and then reach a stable equilibrium instead of continuing to accumulate throughout the photoperiod

Big thanks to @Dennis Wong / 2Hr Aquarist for his articles explaining this approach. I've learned so much from them. It's completely changed how I look at CO₂ injection and surface agitation

For testing I'm using a freshly calibrated Apera PH60 for pH, Hanna Checktemp 1 for temperature, and the Hanna HI3818 CO₂ titration kit to check actual CO₂ concentration. CO₂ kicked on at 12 PM, lights came on at 3 PM, and CO₂ shut off at 8 PM

Tank/water parameters: UNS 60U, Controsoil, RO/DI remineralized with APT Sky, GH 5 to 6, KH 0. My best degassed pH reference is around 7.30, so I'm seeing roughly a 1.7 pH drop at plateau. With 0 KH the standard pH/KH chart doesn't apply, so I'm using the Hanna kit alongside pH to track the curve

Today's testing showed a really good trend. The tank was already at pH 5.60 by 2:30 PM, reached 5.59 at lights-on, and stayed essentially flat through 8 PM. Hanna measured approximately 44 ppm at lights-on and 44 to 45 ppm at the end of the injection period. Since I was essentially at plateau 30 minutes before lights-on, I now feel comfortable reducing my pre-light injection from 3 hours to 2½ hours and seeing if I can still reach the same level by lights-on

My original CO₂ target was around 40 ppm, but at this point I'm wondering if it's worth trying to make a microscopic needle-valve adjustment just to knock off ~4 ppm when the curve is this stable

Would you guys leave it around 44 ppm or bring it down slightly closer to 40?

There's no livestock yet, so I'm taking advantage of this time to get everything dialed in. Plants are doing great. Planned livestock is cardinal tetras, pygmy cories, Amano shrimp, and eventually Caridina, and I'm planning to start stoc
king next week

at KH0, the Hanna kit slightly overestimates the ppm CO2. If it reads 44ppm at 0dKH, you probably have 39-40ppm CO2. Which, with plenty of surface agitation and lack of surface scum, is perfect for high-energy tanks IMO!

 

[TheBurn]

at KH0, the Hanna kit slightly overestimates the ppm CO2. If it reads 44ppm at 0dKH, you probably have 39-40ppm CO2. Which, with plenty of surface agitation and lack of surface scum, is perfect for high-energy tanks IMO!

Thanks Rocco! I actually remember you mentioning in another thread that you compared the Hanna kit against an OxyGuard and found it read about 5–10 ppm high at 0 KH. Was that based on multiple side-by-side tests at 0 KH? If so, that would potentially put my 44 ppm Hanna reading closer to the high 30s, which is pretty much where I was originally trying to land. My only concern with the livestock I've listed is the caridinas. Any input on that aswell?

 

[Naturescapes_Rocco]

Thanks Rocco! I actually remember you mentioning in another thread that you compared the Hanna kit against an OxyGuard and found it read about 5–10 ppm high at 0 KH. Was that based on multiple side-by-side tests at 0 KH?

Yeah, I tested at 0KH, 2KH, and 4KH I believe. I'll have to check my notes, but the Hanna kit overestimated every time compared to the membrane-reading of the Oxyguard, which is independent of water chemistry. Still highly recommend the Hanna kit, as long as we know the limitations and work with them!

If so, that would potentially put my 44 ppm Hanna reading closer to the high 30s, which is pretty much where I was originally trying to land. My only concern with the livestock I've listed is the caridinas. Any input on that aswell?

I've only kept caridina in low tech, 0dKH, but it should be fine. Dennis Wong keeps caridina in many tanks that are CO2 injected to 30-40ppm+, but they all have high surface agitation to keep oxygen high. My thoughts are your shrimp should be fine, just make sure there is lots of O2 in the water separately from CO2 via high surface agitation (and surface skimming of some kind)!