Effects of tannins on KH/pH

Milan

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Sep 28, 2005
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A couple of weeks ago I introduced a mangrove bogwood piece in my tank. I kept an eye on pH and KH over this time and observed something interesting ...

Before the introduction, pH was ~ 6.9 and KH ~ 4. Since than, the KH slowly went up to 10 and pH to 7.3 . I was under impression that tannins from bogwood would lower both of these values, not the other way around :confused: .

Anyhow, by doing some design modifications on the reactor, I managed to increase the CO2 level to about 29-30 ppm, so the pH went back to 7.0, but I'm wondering now if there is something wrong with this picture.

Mind you, the mangrove piece was boiled, and soaked for few weeks prior to introduction to the tank, and there is no visible coloring of the water by leaching tannins.

Can anyone give me some logical explanation?
 

Tom Barr

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Jan 23, 2005
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Re: Effects of tannins on KH/pH

Mangroves are from saltwater, they have lots of salts and that is why the ph/KH went up. It may take soemtime befroe the salts are leeched out.

Regards,
Tom Barr
 

Milan

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Sep 28, 2005
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Calgary, Alberta
Re: Effects of tannins on KH/pH

Tom Barr said:
Mangroves are from saltwater, they have lots of salts and that is why the ph/KH went up. It may take soemtime befroe the salts are leeched out.
Thanks Tom. I makes sense. That wouldn't affect my CO2 calcs, ... right?
 

Tom Barr

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Re: Effects of tannins on KH/pH

Probably not, but SW does have borates and other hydroxides which can add to the alkalinity that is not carbonate alkalinity.

A simple way to check this is to do a huge water change, say 80-90% and then measure the KH right away, set the CO2 rate based on that.

As long as the bubble rate is the same, so will the CO2 level in the tank even if the KH moved around.

This is why using a pH meter alone for using a pH controller can cause problems.

Tap water and tank water change change some and then there is also the issue of non carbonate hydroxides influencing the KH reading.

I'm looking into the non carbnonate hydroxides and a good method to distingush between those and carbonate KH.

I think most test measure total alkalinity.

Regards,
Tom Barr