# Which is the better KH option?



## Martin cape (11 Jan 2013)

Hi guys,

Water out the tap has a KH of roughly 0.5 and a pH of 7.6. So, with me wanting to inject CO2 I decided to increase the KH to 5 to avoid such a large pH swing during injection and when it's off. 

But, I've just checked the pH and its 8.1. So I now have tank water with a pH of 8.1 and a KH of 5. 

But according to this:

AquaScaping World Magazine - Understanding the pH/KH Relationship

When co2 is at its ideal the pH will be 6.8, that's a swing of 1.3 units!!! That seems a lot. 

Whereas if I just stay with the tap water, the pH will change from 7.6 down to 6!!!

Both massive swings. Are they too much of a swing for the fish?


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## Alastair (11 Jan 2013)

Clive pointed out in one of his posts a while back that the ph swing isn't that much of a concern. 
My tap water has a kh of 2 and when I was injecting co2 my ph would drop from 7 to 5.8 during the day with no visible affects to any of the fish. So i tried not to agitate the surface to much which causes the ph to rise at night as your gassing off all the left over co2. 


Sent from my iPhone using Tapatalk


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## Martin cape (11 Jan 2013)

Cheers pal. I won't worry then. 

Ill keep it at 5 though. Don't want it going too acidic.


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## ceg4048 (11 Jan 2013)

It's a waste, not only your time, but also of energy, worrying about pH swings. CO2 is a very weak acid, which means it has a very small disassociation constant and therefore does not release large amounts of protons in an aqueous solution. Amazonian fish often use the pH swings to trigger breeding behavior. Therefore they are not negatively affected by pH swings or by low pH. And certainly, plants do not care at all about water pH.

Cheers,


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## Martin cape (12 Jan 2013)

Thanks Clive. 

Just injected first lot of CO2. Got it up to 15ppm (according to those graphs). So need to increase bubble rate tomorrow. 

Be easier when I get the pub style cylinder. My reg doesn't like this FE.


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