Re: Webb-Kelly tank

> From: ac554 at freenet_carleton.ca (David Whittaker)
> Date: Wed, 9 Aug 1995 09:46:04 -0400
> Subject: Peculiarities of Webb-Kelly tank
> [snip] 
>                 Water Parameters
>                Before       After
> KH (TETRA)      2.0/2.5      3.0
> pH (TETRA)      6.4          7.2
> CO2 injection   x/3 sec      x/2 sec  where x is 1 bubble
> [snip]
> I understand that phosphates and silicates contribute to alkalinity.
> These could be found either in the clay or in the pond tablet fertilizer.
> Does anyone know if this might be the answer? Wouldn't the TETRA KH test
> also falsely measure these as carbonate hardness and so produce a high
> phony KH? Any ideas? The most credible answer receives the Whittaker
> prize in stoichiometry.
> Dave

Oooh I like prizes :). Ok let a newbie try this one. I think you've already 
said it. The slight alkalinity increase is likely due to the phosphate in 
your water. Most KH test kits, likely including Tetras, measure the 
total KH, not just the part that's due to bicarbonate.

Now why does the pH go up so much with such a slight increase in KH? In 
my tank with a KH of ~10, I notice a pH change of 0.2-0.4 during the 
course of a day due to photosynthesis. So it might be that since your KH 
is so low (<3) a slight change in KH or CO2 would significantly affect 
your pH. Is it possible that you have more demand for CO2 since the 
initial setup (due to algae growth perhaps)? 

 John Y. Ching (jyching at watnow_uwaterloo.ca)    |
 Pattern Analysis and Machine Intelligence Lab	| 
 Department of Systems Design Engineering      	| 
 University of Waterloo, Canada            	|