Chemistry

[plantropimunity]

okay so ph is a logarithmic scale of the hydrogen/hydroxide ions in a solution. this i get
kh measures carbonate hardness. this i get
what i dont really get yet is the relationship between these two measurements. i know that when i increase the kh of the water i use for my cichlid tank, ph increases. i dont know why, though.
I am curious as to how i would go about raising kh without affecting ph, if that is possible, because in the tank i am setting up right now, i have a ph of 7.2 and a kh of 2degrees. what i want to accomplish is an increase in kh without increasing ph. i want the ph to be lower, actually. anybody have any ideas?

 

[craynerd]

Since kH and pH are directly related it is impossible to change one without having an effect on the other.

KH as you say is the buffering capacity, the amount of carbonate ions in solution. The more carbonate ions, the greater the waters capacity to with stand changes in H+ concentration, thus pH. It is therefore impossible to change the pH without having some effect on KH and vice versa.

Your best option would be to raise your KH using baking soda to your water when you do a water change. This will ultimately raise your pH so you can bring this down using CO2. The best way to do this will be with a pressurised CO2 system so that you have more control.

Good luck
Chris

 

[Themuleous]

Check you journal

EDIT - nice explanation BTW Chris I must confess to not really understanding it myself, all that I know is that is works! And thats enough for me

 

[anvil63]

good explanation Chris. I always understod equations better than words

H2O + CO2 <--> (HCO3-) + (H+)

CaCO3 + H20 --> (HCO3-) + (Ca++) + (OH-)

(H+) + (OH-) --> H20

H+ lowers ph
OH- will combine with H+ to form water
HCO3 (bicarbonate) is what you measure with a KH test
CaCo3 is baking soda

So how much baking soda you add directly relates to how much H+ is recombined back to normal water.

This also explains why some plants like vals like high Kh values
They directly absorb bicarbonate and make their own CO2
(HCO3-) --> CO2 + OH-

Carl

 

[plantropimunity]

i have read the replies in my journal, and thanks for the quick responses here. i always appreciate the words that accompany the equation, so this has answered in my language. thanks again!!