# CO2 injection leading to large decrease in PH



## Tebo (7 Sep 2012)

Hi,

Newbie to CO2 here, I am getting a large swing in PH each day while my CO2 is on, it's almost 1 PH swing.

Am I injecting too much ? Checker shows the right colour green.

I it because I am not heavily planted yet ? Will heavy planting reduce the swing.

The intention longer term is to host discus in the tank. So need to fix this problem before I even think of that step.

Tank has been running around two weeks now, I have 12 rummy nose tetra at 29C.

Any pointers here would be appreciated.

Thanks
Tim


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## darren636 (7 Sep 2012)

SOUNDS NORMAL, MINE DOES THE SAME- CARBONIC ACID.


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## ceg4048 (7 Sep 2012)

Tebo said:
			
		

> ...I am getting a large swing in PH each day while my CO2 is on, it's almost 1 PH swing.


This is the best possible news.



			
				Tebo said:
			
		

> Am I injecting too much ? Checker shows the right colour green.


Are your fish showing symptoms of CO2 toxicity? If the answer to that question is "no" then the answer to your question is No.



			
				Tebo said:
			
		

> I it because I am not heavily planted yet ? Will heavy planting reduce the swing.


No and No.



			
				Tebo said:
			
		

> The intention longer term is to host discus in the tank. So need to fix this problem before I even think of that step.


There is nothing to fix, unless the discus suffer from CO2 toxicity. They won't care about the pH swings.



			
				Tebo said:
			
		

> Tank has been running around two weeks now, I have 12 rummy nose tetra at 29C.


So..none have been affected by daily pH swings, right?



			
				Tebo said:
			
		

> Any pointers here would be appreciated.


Massive pH swings are a daily occurrence and is normal so you need to get over your fear of pH swings. This is life in a CO2 injected tank.

Cheers,


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## Tebo (7 Sep 2012)

Thanks for the quick replies, this is great news it's nothing to be worried about.

The fish appear to be active and feed well. I don't see anything that concerns me currently.

The concern is more will discus be ok with this level of swing?

Thanks
Tim


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## dw1305 (7 Sep 2012)

Hi all,
Like Clive says you don't need to worry about pH. Have you read this? <http://www.ukaps.org/drop-checker.htm>, it should help. 

It is a bit difficult to explain quickly, but the reason the pH falls is because of "buffering effects" and the carbonic acid ~ bicarbonate equilibrium. The chemistry is here: <http://ion.chem.usu.edu/~sbialkow/Classes/3600/Overheads/Carbonate/CO2.html>





The important bit is that this is an *equilibrium*, as we add CO2 we reduce pH, but we don't reduce alkalinity, and as CO2 levels fall 2HCO3- (bi-carbonate) and Ca++ (calcium) ions will come out of solution as the salt "limestone" = CaCO3, add more CO2 and the limestone will dissolve, releasing bicarbonate and calcium ions, remove CO2 and CaCO3 will precipitate out, on and on for ever in equilibrium (assuming we have some dKH). 

pH swings happen naturally in vegetated soft waters (like some inhabited by Discus), this is from Diana Walstad's "Ecology of the Planted Aquarium"


> Daily variations of the water parameters are rarely – if ever – taken into account. Data collected in a freshwater lake (Star Lake, VT) with a very low alkalinity showed a diurnal pH fluctuation beyond the imagination of most hobbyists. Thus, the pH at 10 am was measured at 5.7 (strongly acidic), 9.6 at noon (strongly alkaline), 8.3 at 2 pm (moderately alkaline) and finally, 6.4 at 4 pm (slightly / moderately acidic). Readings were taken at a 0.5M depth. The fluctuation observed was due to the low KH value of the water (something reported for the Amazon river, too) and the presence of large amounts of phytoplankton. Under the circumstance it is extremely difficult, if not impossible, to figure what is the “right” pH for any form of aquatic life collected in that lake and which tank could cope with this kind of fluctuation. The low – high points of the day differ by 4 pH points, which means that the concentration of H+ in the morning is 10.000 times higher than at noon, while this change takes place in just two hours. It goes without saying that this pH swing cannot be observed in an aquarium only because we cannot reproduce the amount of light which falls in the Lake. In any case, if somebody reported that a suitable pH for aquatic life collected in this lake should range daily from 5.7 – 9.6 most hobbyists would think it was a typo.


From <http://www.plecoplanet.com/forum/showthread.php?t=6901>

cheers Darrel


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## darren636 (7 Sep 2012)

that is intersting reading about the ph swing, eye opening in fact. was wondering about the daily and seasonal changes recently regarding lake inle. almost zero info about what changes happen in water chemistry over the seasons , or a day.


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## Tebo (7 Sep 2012)

Awesome feedback thanks, appreciate the links too.

Thanks
Tim


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## dw1305 (8 Sep 2012)

Hi all,
The problem with pH is that it you need some other values before you can really interpret what it means. 

Whether pH varies much over time depends mainly on the carbonate buffering of the water. If you have very highly carbonate buffered water (water with a high dKH), like in Lake Tanganyika, it would take a huge change in water chemistry (an addition of acids (H+ ion donors)) to lower the pH, which will be stable at pH~8. If you have water with a low dKH, and few other solutes, pH will be a moveable feast and essentially meaningless, and if you have "black water", with a lot of humic acids and tannins and very few other solutes, the pH will remain around pH5, unless we add a lot of bases.

cheers Darrel


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## Tebo (8 Sep 2012)

Thanks, my water is very soft. 

4dKH this explains why I am seeing a large swing.

Thanks
Tim


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## Antipofish (8 Sep 2012)

dw1305 said:
			
		

> Hi all,
> Like Clive says you don't need to worry about pH. Have you read this? <http://www.ukaps.org/drop-checker.htm>, it should help.
> 
> It is a bit difficult to explain quickly, but the reason the pH falls is because of "buffering effects" and the carbonic acid ~ bicarbonate equilibrium. The chemistry is here: <http://ion.chem.usu.edu/~sbialkow/Classes/3600/Overheads/Carbonate/CO2.html>
> ...




Darrel, is that why pH swings CAN be dangerous with very soft water ?  Or how does soft water come into effect in such situations ?


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## dw1305 (9 Sep 2012)

Hi all,


> Darrel, is that why pH swings CAN be dangerous with very soft water ? Or how does soft water come into effect in such situations ?


*Acidosis*
Acidosis and "Old tank syndrome" can be a real problem, but the low pH and fish death are actually both symptoms of what has gone wrong, rather than the low pH causing fish death. 
*pH, the measurement*
The real problem is that pH is such a strange measurement. To get your head around it, you need to think of your water in terms of the amount of H+ ions, the ratio of H+ ion donors (acids) and acceptors (alkali or bases), and the reserve of bases (or dKH). The really important think is that pH isn't a measure of amounts, it is a measure of ratio. 

*pH doesn't tell us anything about amounts, just ratios.*

If I use the scales analogy, in soft water at pH7 you have a sugar cube in either pan (the cubes represent H+ ion donors = "acids" in the acidic pan, and H+ ion acceptors ="bases" in the alkaline pan), the ratio gives you pH, and it is 1:1, 10-7 each of H+ and OH- (O-H) ions



But we will also have pH7 if both pans have a kilo bag of sugar, the ratio is still 1:1, and the pH7. In the soft water case adding a sugar cube of H+ ion donors will reduce the pH down to somewhere near pH4, in the bag of sugar case it will have virtually no effect on pH, because we are talking ratios not amounts. My tap water, which comes out of the tap at about 650 microS, pH7.8 and is saturated with calcium carbonate. To reduce the pH I'd need to add enough acid to neutralise a huge amount of carbonate buffering, in this case even small movements in the pH reflect large changes in water chemistry.

*Carbonate buffering*
Where a low reserve of carbonates can have an effect is in biological filtration, where the conversion of NH3 - NO2 - NO3, uses both a lot of oxygen and a lot of carbonates. If you have a very low reserve of carbonates (dKH), pH values will be unstable. Another problem you may have is that heavy metals like copper (Cu++) will be potentially in solution at acid pH levels, and again these may effect both fish and biological filtration. 

*Old Tank Syndrome*
If you don't change very much water volume, the natural processes in the tank over time will reduce the pH and the reserve of carbonate buffering. This is "old tank syndrome", which was a common problem in the 1970's, where most people didn't change their water, and old tank water was supposedly full of magical properties, and fresh water was thought to be actively dangerous, I started fish keeping then and killed all my fish fairly quickly. 
There is a good explanation here by the ever erudite "Skeptical Aquarist": <http://www.skepticalaquarist.com/bioacidification>

This is the stable, highly carbonate buffered, hard water scenario, where even though the "lowers the pH" side will grow larger over time, it will always be a tiny fraction of the "raises the pH" buffering.





and this is what happens to the pH when the dKH (conjugated base reserve)is exhausted.





cheers Darrel


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## Soilwork (2 May 2016)

Thanks Darrel.  That's cleared a few things up on kh/ph equilibrium.

So what are the implications of low ph on our nitrifying bacteria? How do bacterial colonies in freshwater that are exposed to such low ph levels react?  Are there different species that grow at different ph levels? 

Are plants/algae the major players in ammonia removal?


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## dw1305 (2 May 2016)

Hi all, 





Soilwork said:


> So what are the implications of low ph on our nitrifying bacteria? How do bacterial colonies in freshwater that are exposed to such low ph levels react? Are there different species that grow at different ph levels?


It depends on the context, at low pH levels you will get a different suite of micro-organisms involved with nitrification. I think that aquariums with some carbonate buffering are easier to manage, but if you have planted aquariums this is much less relevant. 

Most of the older literature (both scientific and hobby based) assumes that nitrification in aquaria is largely carried out by a very limited suite of nitrifying bacteria. We now know that isn't true, and that much (all?) of the nitrification in aquaria is carried out by Archaea, and that nitrification occurs over a much larger range of pH values than we had traditionally assumed. Across a range of pH levels Archaea look to be the dominant ammonia oxidising organisms, and the bacteria (_Nitrospira_) the organism responsible for the conversion of N02 to NO3. 

<"Recent research"> has shown that _Nitrospira_ can potentially perform both the oxidation of ammonia, and the conversion of NO2 to NO3, but I don't think any-one has found out, yet whether this is true in aquarium biofilters. It is a fertile area for research so I would expect that more novel organisms and paths for nitrification will be discovered.

Have a look at <"Raising the pH.....">.

cheers Darrel


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