Co2 adjustment with PH-meter

[robin.weiss]

Hi,

my name is Robin and I am relatively new to the Aquascaping hobby after having tanks for a little over 2 years now.

In my 112l tank I use an external reactor to suplly CO2 and have a PH-Controller with it. It is set to 6.5 PH (hysteresis is 0.1PH). With KH 3 (tested by a drop test kit, which is not accurat as I learned here) I should have around 30ppm CO2. It is switched of at night.

My question is:
During the day the system is switching on and off naturally, so I have no constant input of CO2, just an almost equal level between 24ppm and 30ppm (according to the Dennerle CO2 table at least.)
Is that the right way?
Is it better to use an internal reactor that constantly sprays CO2 bubbles in the tank?
How would I set the right amount of bubbles with a drop checker?
If the system is set to eg. 35 bubbles/minute for the whole day I would have a high variance in CO2 level during the day.

Thanks for sharing your knowledge. This site is helping me more than anything before to understand things.

Robin

 

[Tom Barr]

I think most folks use a semi automated method for CO2, both Amano and myself suggest that method, add CO2 during the day time only.
We both arrived at the conclusion independently.
But because I do agree, does not mean I agree with everything he says, but it's a good bet if we both agree, then it's likely to be a good method.
Other items we both suggested: large weekly water changes and dosing thereafter frequently.

There is no advantage adding CO2 at night, plants do not use and fish sure do not like it when the O2 levels are also lower due to plants not producing O2.

When you do add CO2 during the day, you can add more as the fish also have more O2 from the plants during that time and there is less chance of CO2 build up.

We add CO2 to fertilize the plants, not to control pH, that is just used from measurement.

With a good CO2 system, you can do it only with the lights on.
Many add CO2 about 30-60 minutes before the lights come on and shut it off about 30-60minutes before the lights go off.

That way there is plenty of CO2 as soon as the lights come on till night time.

This method saves CO2, less risk to livestock, simpler etc.

Regards,
Tom Barr

 

[neil1973]

I use a ph controller on a planted tank but paid little attention to the kh/ph tables and am not bothered about actual ph value although I do calibrate the controller now and again. I use the controller as a means of hitting a certain co2 level based on the response of the fish. What I do is decrease the ph set point slowly (e.g 0.1 units per day) and carefully observe the fish for signs of stress e.g. increased respiration, at that point I then back off by about 0.2 ph units. The whole system can be linked to a timer so the process only takes place while the lights are on and this will give the benefits that Tom mentioned. You will find that the fish are most likely to show signs of stress at the beginning of the day when the lights haven’t been on long and O2 levels are lowest. If you are going to use this method then it is worth making sure your ph probe is in reasonable condition and responsive, and please take it very slowly and be careful with your fish.

Cheers
Neil

 

[Tom Barr]

Neil's relative approach is the wisest method using a pH controller, and still use it. You get the relative usage, the part that actually counts.

Like adjusting the bubble rate with a needle valve to hit that relative pH, you still use the same needle valve without the pH control to adjust CO2, you just use a bubble rate instead.

The bubble rate is relative a ball park amount as well.

The best methods we have for measuring CO2: the pH meter/KH reference and the pH KH ref solution drop checker.

Even those could be considered relative since we often add as much CO2 as we can without pestering the fish, that is different for many different species/tanks etc.

Regards,
Tom Barr

 

[vidiots]

I've had this idea for a while that I just haven't tried yet. I've been considering adding a cheap low range flow meter to the output of my CO2 bottle. I would then adjust the CO2 flow until the PH of the water is where I want it then record the flowmeter reading for future use. Then when I change out the bottle I can just adjust the valve until I get the same flow rate as I had before. I was thinking this might be easier and more consistant than a bubble counter. Not only that on my big tank the bubble rate thru my bubble counter is too fast to count.

I know that Dywer Instruments makes some very cheap little plastic flow meters that only cost a few dollars and are accurate to 10% or better.

Any thoughts on this?

 

[VaughnH]

I know of no flow meter capable of measuring the tiny, tiny flow rates we use for CO2 injection. When you are talking about 2 bubbles per second that is about 0.00001 cfm, way below the range of flow meters.

 

[vidiots]

I know of no flow meter capable of measuring the tiny, tiny flow rates we use for CO2 injection. When you are talking about 2 bubbles per second that is about 0.00001 cfm, way below the range of flow meters.

Good point I knew it was low flow, but didn't take the time to guestimate how low of a flow.

Now I've put some thought into it, and looking at my bubble counter I estimate the bubbles to be about 3mm in diameter. When you calculate the volume of a sphere with a diameter of 3mm you come up with 0.0141 cm3. Then if to put it in common units you figure 2 bubbles per second for 60 seconds you get 1.692 cm3/min. This is an extremely low flow.

They do make flowmeters in this range, but they are not the cheap ones I was thinking about. I'm figuring you'd want one with a range of no more than 10 cm3/min and a resolution of at least 0.2 cm3/min or better.

Oh, well it was a thought...

I think it would be neat if they made low range Thermal Mass Flow Controllers in the price range a hobbiest could afford.