How does CO2 do with active buffering substrate?

[Akio]

Hello,

I'm honestly a bit confused regarding the relationship of ph/kh/co2 even after plenty of research. As of right now, my tank has no co2 injection and is currently using Tropica AquaSoil. This soil brings down the KH and pH. My tap water is already next to 0KH and 6.8pH, and the substrate brings it down to some tiny KH number (0.0???) and 6.4pH.

From my understanding the lower the KH is, the less CO2 is in the system (holding pH constant). If my KH is practically 0.0 due to the active substrate, wouldn't that suggest that the CO2 levels are essentially non-existent, and that any CO2 injection won't really change the CO2 level?

Even if my KH isn't exactly 0.0, say 0.1 or 0.2, wouldn't getting a CO2 to any decent level (say 15ppm) require an insane change (more than 1 point for sure) in pH? I don't necessary need to get my CO2 to 30ppm, but having it get to 10 or 15ppm would be nice, but I'm concerned about the drastic pH fluctuation. Has anyone had experience working with active substrate that brings KH down to the zeros?

[ZxC]

No, KH does not determine how much CO2 is in the water, atmospheric CO2 concentrations or the rate and efficiency of pressurized CO2 system determine how much CO2 is in the water.

The KH/pH/CO2 chart you are referring too is not accurate, and is best used as a ballpark reference point only. It cannot be used at all for tank with a buffering substrate.

Your CO2 concentrations at the beginning of your photoperiod are 3-4ppm if you are not running a CO2 system.

Active substrate are designed to bring KH down to 0 because that's what plants prefer, the substrate acts as a buffer for pH swings, and releases humic acids to bring pH down to the mid 6's. This is best for plants because that is the pH where most nutrients are readily available for plant uptake. Your source water is perfect for using active substrates, because it already contains very little KH, meaning a long and consistent life for your substrate.

[Akio]

After reading your post and a few other archived posts I think I understand. It seems I've fallen for the KH CO2 myth.

Is there any resource I can use to give an accurate estimate of how much my pH will be lowered by going for x ppm that takes the active substrate into account?

I'd like to figure this out before I determine what fish/shrimp I'd like to get.

[Brookster123]

And we thank zxc for that contribution. I have conveniently removed all things co2 related from my fish brain.

[ZxC]

Originally Posted by Akio

Is there any resource I can use to give an accurate estimate of how much my pH will be lowered by going for x ppm that takes the active substrate into account?

I'd like to figure this out before I determine what fish/shrimp I'd like to get.

Not that I know of as far as I'm aware. What you can do is use a drop checker, they are a ballpark reference tool as well, but if you get it to a lime green, almost yellow, that will be 30-40ppm of CO2 in the water.

In tanks without active substrates, we use pH drop to determine CO2 levels. A 1.0 drop in pH from CO2 = roughly 30ppm of CO2. There is a math formula for this, but we just watch the pH drop. 1.0 - 1.4 seems to be safe for fish and shrimp, so long as you work up to these numbers over a few weeks to allow the livestock to adjust if needed. When running this high amount of CO2, we like to keep surface agitation high to allow for good gas exchange, and some of us run airstone at night to quickly saturate the water with O2 again / off-gass CO2 that is not needed after the lights shut off for the day.


Your best best would be to use a drop checker, get it lime green / almost yellow, and then note your pH. Try and keep it as consistent as you can during the photoperiod. Plant cells prefer consistent CO2 concentrations.