Low KH questions

[Eddiekay1010]

When working with soft water(low KH/GH, Conductivty), do you worry about ph crashes due to the lack of buffering abilities of having a low KH. How can you help prevent pH crashes when working with soft water. Please correct me if I'm wrong, never went past high school chemistry and that was a long time. KH is what buffers the water to prevent pH crashes right, and you can't have soft water without a low KH. Sorry for all the questions but a low conductivty and a low KH/GH go together right, they all move together in the same direction and you can have a neutral to slightly high pH with soft water? Just trying to wrap my head around all this, thanks

 

[dw1305]

Hi all,

How can you help prevent pH crashes when working with soft water. Please correct me if I'm wrong, never went past high school chemistry and that was a long time. KH is what buffers the water to prevent pH crashes right, and you can't have soft water without a low KH.

That is it, soft water has very little carbonate buffering (dKH), so any small addition of acids (or bases) will cause large fluctuations in pH. <"This is not a problem">.

they all move together in the same direction and you can have a neutral to slightly high pH with soft water?

You can, if you use a strong base like sodium hydroxide (NaOH) it doesn't add any buffering or dKH (or any dGH) but it will raise the pH. You don't need to add very much NaOH, which is another reason why conductivity is of more practical use to us than pH. With pH you always need to know some other parameters before you can interpret what it actually means. I just think <"pH and buffering are quite difficult concepts">, particularly as you can't extrapolate from hard to soft water.

If you get the pH falling in heavily buffered water, it represents a major change in ionic water chemistry. The problem is with the "pH crash" concept, if you get acidosis and fish death they are both symptoms of other problems, the one hasn't caused the other. I just try and avoid major changes in water chemistry, changes in the ionic content of the water.

I'm not, nor have I ever been, an aquascaper, but <"some of my friends are">. Every day they add pressurised CO2 to their tanks and the pH drops by one unit (when you have ~30ppm CO2). At the end of the photo-period the CO2 goes off and the pH rises by one unit, often pretty rapidly. Many of them <"have very healthy fish">.

This <"diel pH variation"> occurs naturally in soft vegetated water. This is from: Rocha, RRA.; Thomaz, SM.*; Carvalho, P. & Gomes, LC. (2007) Modeling chlorophyll-α and dissolved oxygen concentration in tropical floodplain lakes (Paraná River, Brazil) Brazilian Journal of Biology 69:2

cheers Darrel