CO2 1 pH drop and aquasoil

[artaqua]

Hello,

First of all I really love this forum and it helped me a lot in my aquascaping journey.

However, i'm struggling to have a clear answer on a point :
I read many times that the sweet spot of CO2 injection is a 1 pH drop.
But, is that really achievable when using an aquasoil that buffer KH/pH ?
In my case, i'm using the Tropica Aquasoil (pretty new, nearly 2 months) and even with an high injection rate my pH seems to be stuck at ~6.

I will love some clarification on this point when using buffering soil.
Thanks in advance for your help

 

[Zeus.]

Aquasoil (AS) with its Cation exchange capacity (CEC) buffers the tanks nutrients and pH, there can be a decrease in pH with some AS and this is normal. This drop in pH can be beneficial esp when your tap water is on the hard side as the decrease can improve the Fe availability to the plants.
When it comes to injecting CO2 however I have never heard of issue or had one myself and I have used AS and managed a 1.0pH+ without an issue.
As for high injection rate here a vid of my injection rate in my 500l tank

I use to adjust the working CO2 pressure to adjust the injection rate as counting bubbles seemed fruitless

The colour change of the Drop Checker (DC) is the best indication of [CO2]

 

[Bradders]

I had this 'problem' as well. Tap water was pH7.6, aquarium water with Tropica Aquasoil was pH7. So where is the 1pH drop?

In the end I done two things:

1. Took the average between the aquarium water and the tap water. (pH 7.3, so aimed for pH6.3 for 1 pH drop method).
2. Used my Dropchecker to ensure it was lime green when reached pH6.3 (i.e. not too little, not too much).

The drop checker is the important part, as the 4dKH solution separated by an air gap from the water. The CO2 has to cross the air gap so you know its measuring CO2 without having to worry about the pH of the water.

 

[artaqua]

Hey,
Thanks for your answers !

So, if I understand, the 1 pH drop is totally achievable even with aquasoil.
Whats strange and bothering me is that even with pretty high injection (5 bps Proflora Inline integrated counter, that seems MASSIVE for only 30 gallons) I never reach the 1 pH drop.

Using RO water, my tank fully degazed pH is ~6.5/6.6, with injection I can’t drop below 6 which is, at the best, only 0.6 pH drop…

 

[Andy Pierce]

If you are injecting CO2, then only the pH drop caused by injected CO2 counts. Decreasing the pH by equilibrium methods other than CO2 injection doesn't change the levels of dissolved CO2 gas in the water column, although the decreased pH might be beneficial for other reasons. So if the non-CO2-injected pH of your aquasoil aquarium is water 7, you'd be looking for CO2 injection to shift the pH to 6, representing in a 10x increase in the levels of dissolved CO2. It doesn't really matter what the pH of your tap water is. In any case, the drop checker is your more definitive readout.

To your CO2 losses, these can be reduced if you have a lid/cover on the tank (this helps a lot) or if you turn down/off aeration (not recommended) or if you get a finer spray of CO2 bubbles using a better diffuser - I use a Twinstar CO2 diffuser. You can also keep the finer CO2 bubbles in the water column for longer if you position the CO2 diffuser at the bottom of the tank and ideally right next to or under a powerhead or other water flow output so the bubbles are swirled around in the water column instead of rising directly to the surface. You could also consider whether your method of measuring pH is really doing what you think it is doing... this isn't actually trivial to measure.

 

[dw1305]

Hi all,

..... If you are injecting CO2, then only the pH drop caused by injected CO2 counts. Decreasing the pH by equilibrium methods other than CO2 injection doesn't change the levels of dissolved CO2 gas in the water column ......

(Tank) water is (pH) 7, you'd be looking for CO2 injection to shift the pH to 6, representing in a 10x increase in the levels of dissolved CO2. It doesn't really matter what the pH of your tap water is. ........

In any case, the drop checker is your more definitive readout ......

You could also consider whether your method of measuring pH is really doing what you think it is doing... this isn't actually trivial to measure.

Perfect.

I was just about to post my own, much less coherent (and probably scientifically jumbled), answer to this question, but now I'm going to remember @Andy Pierce's <"answer">, so that I can refer any-one, who ever asks this question again, to Andy's post.

cheers Darrel

 

[artaqua]

If you are injecting CO2, then only the pH drop caused by injected CO2 counts. Decreasing the pH by equilibrium methods other than CO2 injection doesn't change the levels of dissolved CO2 gas in the water column, although the decreased pH might be beneficial for other reasons. So if the non-CO2-injected pH of your aquasoil aquarium is water 7, you'd be looking for CO2 injection to shift the pH to 6, representing in a 10x increase in the levels of dissolved CO2. It doesn't really matter what the pH of your tap water is. In any case, the drop checker is your more definitive readout.

To your CO2 losses, these can be reduced if you have a lid/cover on the tank (this helps a lot) or if you turn down/off aeration (not recommended) or if you get a finer spray of CO2 bubbles using a better diffuser - I use a Twinstar CO2 diffuser. You can also keep the finer CO2 bubbles in the water column for longer if you position the CO2 diffuser at the bottom of the tank and ideally right next to or under a powerhead or other water flow output so the bubbles are swirled around in the water column instead of rising directly to the surface. You could also consider whether your method of measuring pH is really doing what you think it is doing... this isn't actually trivial to measure.

Hey Andy,
Thank you very much for your well detailed answer !
In my case I do not measure the tap water (or RO water as I only use RO water).
I let sit tank water for ~48h, have a reading of 6,5/6,6 pH fully degazed and measure a ~6 pH during injection.

Anyway, if I understand correctly nothing can really buffer the pH and I should be able to have a fully 1 pH drop (which is not the case even if my drop checker looks lime Green).

The finality of all this questioning is that I think that I possibly have an inconsistent CO2 level which can explain my BBA

 

[Andy Pierce]

Anyway, if I understand correctly nothing can really buffer the pH and I should be able to have a fully 1 pH drop (which is not the case even if my drop checker looks lime Green).

If you get the drop checker set up correctly and the colour of the drop checker says you have 30 ppm CO2, then you do have 30 ppm CO2 and at that point I just declare victory. If in your system that works out to a pH drop of 0.6 units instead of 1.0 units, I still declare victory. In general I think for improved plant growth without hurting livestock there is a pretty wide range of acceptable CO2 levels, maybe anywhere between 10 ppm and 45 ppm is fine so you don't need to be too fussed about trying to very precisely hit a magic numerical value for the pH drop. You can put in a fast-growing stem plant as a temporary indicator of how well plants can grow in your set-up, maybe Hygrophila polysperma would be a good choice. If you find you have to pull handfuls of the stuff out of your tank every other week because it's growing so fast you know you're in a good place for CO2 (and all other nutrients).