# Re: [APD] RE: Optimum nutrient levels -- Buff that tank untill thetable shines

```Gosh, start talking chemistry (always a risky business for
me) and you sure find out where the woodwork is ;-) Just

Here's the thing I had in mind. It's from Roger from a few
osts some time ago on APD and was included in TAG (Vol 15
No.1, pp 22-24). I have gotten Roger's meaning wrong? Oh,
that couldn't be could it? :-\  So, here's the text and
folks can get it straight from Roger's words. I ofer it not
in refutation, but only for consideration:

"While there are conditions that mess with the KH-pH-CO2
table, the amount of phosphate [she] is adding to her tank
will not cause a problem. That is, unless the phosphate
level builds up to 10's of ppm or more and the KH is very
"
and further info comes with this table and Roger's
explanation of how to apply it:

"
pH   conversion pH  conversion pH  conversion  pH conv.
ppm/degree     ppm/degree      ppm/degree    pm/degree

5.0	341	6.0	147	7.0	72    8.0    48
5.1	312	6.1	136	7.1	68    8.1    46
5.2	286	6.2	127	7.2	65    8.2    45
5.3	262	6.3	118	7.3	62    8.3    44
5.4	240	6.4	110	7.4	59    8.4    43
5.5	221	6.5	103	7.5	57    8.5    42
5.6	203	6.6	96	7.6	55    8.6    41
5.7	187	6.7	90	7.7	53    8.7    41
5.8	172	6.8	85	7.8	51    8.8    40
5.9	159	6.9	75	7.9	49    8.9    39

For example let's say that you have pH=6.8, KH=3 degrees
and PO4=3 ppm. The conversion factor for a pH of 6.8 is 85.
The KH contribution from a PO4 concentration of 3 ppm/85
or 0.035 degrees.  At this point you ask yourself if it
makes a difference, and the answer is "No".  Going on with
the example anyway, the correct KH is 3-0.035 or 2.965
degrees.  Use KH=2.965 in the pH-KH-CO2 chart, table or
formula.

Obviously, you have to have a *lot* of phosphate in
solution to make much of an impact on the measured
alkalinity, and the pH in your tank has to be pretty high
for it to make any difference.

The chances of getting interference from organic acids
appears to be far higher than the chance of a problem
arising from phosphate concentrations. "

Scott H.
--- gbooth at frii_com wrote:

> I'm not sure how to quantify "a whole lot" but here is an
> example. If you
> use commercial pH adjusting compounds that contain
> your pH, you are adding enough to throw off the tables -
> by definition.

=====
S. Hieber

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