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Hey all, Happy New Year! I am looking for some general advice on dialing in my CO2 a bit better. I know every tank is different but I'm definitely struggling with whether to use the 1 point PH drop, drop checker color or the CO2 table. I'm using a PH probe connected to my Apex controller to monitor PH (Its calibrated every couple of weeks and it matches my PH Pen, which is calibrated at the same time). I'm probably misunderstanding a key point of how to go about this or how to use a particular piece of information so I'm hoping someone can point me in the right direction.

Tank: 55G, moderately planted, heavy if it let it grow out
GH: 6
KH:4-5
TDS:140
PH 6.67 when CO2 turns back on the next day, 7.2 if I off gas a cup of tank water.
Lighting: chihiros wrgb 2
Subrate: uns controsoil
Water changes are with RODI water reconstituted with a bit of Aquavitro Carbonate
Moderate Surface agitation from lily pipes and a powerhead
CO2 runs from 11:30AM - 8PM and lights run from 1pm to 9pm

No ferts right now although I'll be going to PPS Pro once I have Co2 dialed in.


My KH is naturally high due to the fact that I have some lava rock and Siryu stone in the tank that seems to leach some carbonate, I'm not too worried about it and I've just learned to live with it. I may be able to knock it down a bit more with aggressive water changes but since overall the tank does well, I don't see a need.

So here is the root of my question: I run about 3 BPS of CO2 on the schedule above. This takes my PH down from 6.67 to around 6.4 when the lights come on and it continues to fall to about 6.2 through the light period and finally levels out. Drop checker is generally green, trending toward yellow, fish are all fine.

If I'm going off the 1ph drop that means, I would have to probably close to double the CO2 from 3 BPS to 6 BPS which seems incredibly high to even get close to the 1 point drop by the time the lights came on, I also feel like that would be a ton of CO2. If I use the Co2 table, I believe I'd need to be around 6.5 PH which is a very small drop. But I'm not sure if I should be using the 7.2 number that I get if I off gas a cup of water or the 6.67 I get in the tank right before CO2 turns back on for the day. Either way, I'm clearly not getting there fast enough since I never see PH stabilize until almost right before the Co2 goes off.

Really my goal is to get it to a point where the drop is in the right range and the PH stays table throughout the day but I've not been able to get to this yet. Advice?

Thanks,
Steve
 

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check this out, especially the "surface agitation and gaseous exchange in co2 injected plants" section.
 

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Here is how I understand the articles. Im also in the same boat as you rn, but I figured I could offer my current thoughts on it.

In short, to reach your target ppm faster you need to increase the rate you’re injecting Co2, this will aid in keeping the co2 levels stable during the photo period. The problem is, unless you also have good gas exchange and off gassing, ur likely gonna gas ur fish.

this is what Dennis is talking about in the 2hraquarist page around optimizing co2. otherwise, your Co2 will follow a curve similar to what you have now, where it ramps slowly, and at some point during the photo period, it reaches its equilibrium point, where the amount of Co2 being off gassed is equal to the Co2 being dissolved.

this is why you start Co2 hours before the lights turn on, so there is enough time for the Co2 levels to ramp up. But if you say have crazy fast off gassing and gas exchange, you can inject at a faster rate, which gives you that sharp change in pH and reach the equilibrium point faster. At some point, it won’t matter how much ur adding, as it will off gas just as quickly, and this allows ur Co2 to be stable during the entire photo period.

Have you considered starting the Co2 sooner? Like at 9-10 AM? Then it could reach more optimal levels when lights initially turn on.
 

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You should be comparing your offgassed figure of 7.2 to your lowest figure while CO2 is running (6.2).

So, you are already hitting a 1 point drop during your lighting period. It sounds like you should maybe just have it turn on earlier so you're at one point when the lights turn on.

You also may find that you want to run a bit more CO2. A 1.2 drop seems to be a nice zone for a moderately high light tank. Some go as high as 1.4-1.5. the more you push it, the more sure you have to be that your gas exchange is on point.
 
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