# Preferred CO2 levels and gas exchange



## Jaap (24 May 2015)

Hello,

What is considered to be more beneficial? 

1. Injecting CO2 some time before lights on and until lights off, but because there is minimal water surface agitation then CO2 is kept in the water and dropchecker is 24/7 lime green even when CO2 is off.

2. Injecting CO2 some time before lights on and until lights off, but because there is water surface agitation the CO2 is degassed and the dropchecker goes from lime green to blue once the lights are off.

Thanks


----------



## Iain Sutherland (24 May 2015)

Surface movement is more important than people give it credit for.  You will find it very difficult to maintain good co2 levels from lights on without stressing you fish later in the light cycle unless you have good surface movement.  A nice gentle rippling is key IMO.


----------



## RossMartin (24 May 2015)

Iain Sutherland said:


> Surface movement is more important than people give it credit for.  You will find it very difficult to maintain good co2 levels from lights on without stressing you fish later in the light cycle unless you have good surface movement.  A nice gentle rippling is key IMO.



I agree with this 100%! I could only get a good and sustained CO2 level in my tank by increasing surface movement!


----------



## Jaap (24 May 2015)

RossMartin said:


> I agree with this 100%! I could only get a good and sustained CO2 level in my tank by increasing surface movement!


Actually this could not be true...I mean its easier to get co2 levels up when surface movement is low...I am guessing you are trying to say that you could get a good and sustained level of co2 and oxygen with surface movement...I might be wrong so forgive me...


----------



## Marcel G (24 May 2015)

Here's probably what you are looking for: http://www.prirodni-akvarium.cz/en/technikaCO2nastaveni





Without surface rippling your CO2 levels can increase up to some dangerous levels later at the light cycle (up to 80 ppm in my case). When you add rippling, your CO2 level will be somewhat lower, but at the same time more stable and constant during the whole photoperiod (40 ppm).

Also if you use for example 1 bps, the increase of CO2 concentration will be slower (more shallow) then in case you use 3 bps → in that case the increase will be steeper (like on the picture).

So what you want is:
1) More bps for quick increase of CO2 level to the desired level (for example, at 1 bps your CO2 gets to 30 ppm after 4 hours, while at 3 bps you achieve the same level in 2 hours).
2) Surface rippling for maintaining the uniform/stable/balanced CO2 level during the whole photoperiod.

PS: As you can see from the picture, aeration (using air stones) is not as effective as surface rippling.


----------



## RossMartin (24 May 2015)

I had issues getting the PH to drop by one PH point and then keeping it there. I only achieved this when i raised the spraybar to give me more surface agitation.


----------



## Jaap (24 May 2015)

ardjuna said:


> Here's probably what you are looking for: http://www.prirodni-akvarium.cz/en/technikaCO2nastaveni
> 
> 
> 
> ...


Ardjuna saves the day 

So we need surface agitation to prevent high and lethal co2 levels? 

Why wouldnt we want 1bps lets say for 3 hours to reach 40ppm and when lights on to remain at those levels rather than 3bps 1 hour to reach 40ppm and then surface agitation to keep at safe levels? 

thanks


----------



## Christos Ioannou (24 May 2015)

@ardjuna is it a direct measure of co2 ppm or you do a conversion from pH to co2 ppm for what you are presenting in the chart? (The pH line seems to be a straight line).


----------



## Marcel G (26 May 2015)

Jaap said:


> So we need surface agitation to prevent high and lethal co2 levels?
> Why wouldnt we want 1bps lets say for 3 hours to reach 40ppm and when lights on to remain at those levels rather than 3bps 1 hour to reach 40ppm and then surface agitation to keep at safe levels?


1) In a sense, Yes. But if you lower your "bps" (bubbles per second rate) you lower the CO2 concentration also, so with (say) 1 bps you won't get to 80 ppm like with 3 bps.
2) Without rippling your CO2 levels will probably increase no matter what "bps" you have. So even with 1 bps your CO2 levels will continuously rise, and won't stop at the desired level but will keep to rise over this line. So the only difference between 1 bps vs. 3 bps (only example values!) will be slower or faster increase of CO2 levels in your tank.


----------



## Marcel G (26 May 2015)

Christos Ioannou said:


> @ardjuna is it a direct measure of co2 ppm or you do a conversion from pH to co2 ppm for what you are presenting in the chart? (The pH line seems to be a straight line).


Of course, it's indirect calculation of CO2 based on known pH and HCO3 concentration (carbonate alkalinity). No one here has probably CO2 meter as this device costs approx. £1950 ! The CO2 values calculated by this method can be a little overestimated (if total alkalinity is not made by bicarbonates only), but the curve (the principle) is what matters here, not the exact data.

_PS: If you want precise calculation of free CO2 in your tank, you can analyse your water to find out what's your TIC (total inorganic carbon). From this value you can quite precisely calculate the mutual ratio of CO2:HCO3:CO3 in the water (in a much better and reliable way that from KH only) based on pH._


----------



## Christos Ioannou (26 May 2015)

ardjuna said:


> Of course, it's indirect calculation of CO2 based on known pH and HCO3 concentration (carbonate alkalinity). No one here has probably CO2 meter as this device costs approx. £1950 ! The CO2 values calculated by this method can be a little overestimated (if total alkalinity is not made by bicarbonates only), but the curve (the principle) is what matters here, not the exact data.



Hi thank you. I have been visiting your site and I would not be surprised if you had one, since your work is taking this hobby to another level!  
Is this formula you are using something you can share? Does it reflect on drop of 1ph unit = 30ppm co2 concentration?

Thanks!


----------



## Marcel G (26 May 2015)

Christos Ioannou said:


> Is this formula you are using something you can share? Does it reflect on drop of 1ph unit = 30ppm co2 concentration?


The formula to calculate the free CO2 (as well as CO3 form of carbon) from the pH and HCO3 concentration is extremely complicated one (if you want to do it precisely). For this reason, I made an online calculator (with the help of some chemists), so that anyone intrested can calculate it for his tank. You can find it here:
http://www.prirodni-akvarium.cz/en/vodaChemie2
You can fiddle with different values and see how it affects the CO2:HCO3:CO3 relationship.
Here, I would like to appeal to use this calculator only with the real values measured in your tank.
Let me show you an example of how you can get wrong results if you don't use it correctly:
1) In the tank with a pH 6.7, temperature 25°C, carbonate alkalinity 4°dKH and zero salinity, you get 28 ppm CO2, 87 ppm HCO3 and zero ppm CO3 in your water; and total inorganic carbon concentration (TIC) of about 2 mmol/l.
2) If you lower the pH to 6.4 in the calculator and leave other values as they are (i.e. pH 6.4, 25°C, 4°dKH, 0 ‰ salinity) you get 56 ppm CO2, 87 ppm HCO3 and zero ppm CO3; but the TIC will increase to 2.7 mmol/l.

This is in reality not possible without adding some source of carbon into your water (like CO2). You can lower your pH also by adding some non-carbon acid (like HCl); and in such a case the TIC won't change. So it's important to know this when you use the calculator. It gives correct data only if you lower the pH by adding more CO2 (in the form of H2CO3) or HCO3 (in the form of baking soda [NaHCO3] or other HCO3 compounds). I think it can help you understand what's going on in your tank when you add more CO2 or raise your carbonate alkalinity.
As you will see, adding more CO2 into your tank (i.e. decreasing pH in the calculator) won't change your carbonate alkalinity (i.e. concentration of HCO3 ions). At pH 6.7 the concentration of HCO3 is same as at pH 6.4 (87 ppm). What changes is the concentration of free CO2 (from 28 ppm at pH 6.7 to 56 ppm at pH 6.4). Also what logically changes is the mutual ratio of CO2:HCO3:CO3 ions, and the total inorganic carbon concentration (as with lower pH you have added more CO2 into your tank, so now you have more carbon in your water).

Marcel


----------



## Victor (3 Aug 2015)

What are the concerns to keep a weak surface agitation and get surface scum? My water surface is covered by a film that makes the water agitation even weaker. So I think the gas exchanges is severely affected. I'm injecting a massive CO2 amount in my tank because I haven't fauna yet. So my 6 dkh drop checker is always yellow during all day and all night at substrate level. It never turns green. What's the consequences of this? Should I get rid the surface film? If yes, how? Thank you.


----------



## ian_m (3 Aug 2015)

Victor said:


> Should I get rid the surface film? If yes, how?


Air stone on after lights off did it for me. Made drop checker go blue by morning and no surface film. Done.


----------



## milla (3 Aug 2015)

Option 3: 24/7 Co2 good surface agitation.  Removes any chance of issues due to fluctusting Co2 levels.


----------

