Cheap mix, CO2 and KH testing

Kevin Conlin writes concerning the Chelated Micronutrient Mix.....

>I'd like to know what else is in there too.  The label only accounts for
>about 55% of the trace element mix.

It's puzzled me for quite some time.

>My cardinal tetras had a habit of eating the powder before it dissolved,
>and I can't imagine that being particularly good for them.

It should give them a nice metallic shine.

Joanne Stevens responds concerning CO2 testing methods.....

>> The best method of which I am aware is to titrate a fresh sample with
>> sodium carbonate (N/22). Free CO2 combines with NA2CO3 to form NaHCO3
>> which is colourless in the presence of phenolphthalein indicator. The
>> sample turns red at the point at which no free CO2 exists and excess
>> Na2CO3 is present. It is then a matter of calculating the result. If
>> one is careful, the result is fairly accurate. Free mineral acid, if
>> present, will be measured in the test. The lab equipment will cost you
>> a few bucks though. Seems a bit of a bother to me.
>> ppm free CO2 = ml N/22 sodium carbonate X 1000/ml sample

>Either this also works with sodium hydroxide or else Dave has his chemicals
>slightly mixed up.  The La Motte kit works on this principle using a dilute
>sodium hydroxide solution.  I have found that the La Motte kit CO2 readings
>agree very well with the table, especially when I use 10 or 15 mls to do my
>KH reading & divide it by 2 or 3 to get a more accurate value (as suggested
>by George) and use a pH kit that distinguishes pH within 0.1 unit.


There is no mixup. It is a different test. I had never seen or heard described
the LaMotte test, and thought that it might be a 5 ml sample vial to which one
adds drops from a bottle, much like the Tetra pH test kit. This method is the
most accurate of which I am aware, and was used by a firm that tests and treats
industrial water. It is probably not cost effective unless you are doing a lot
of testing. The LaMotte product sounds excellent at $14. I should mention that
salts of iron, chromium, aluminum and other metals interfere with the test. I
don't know to what extent. Would this be true of the LaMotte test as well?

Some people were complaining about shelf life. Which titrating solution is the
more stable, sodium hydroxide or sodium carbonate?

One comment concerning testing for KH. I cannot see how one could ever be sure
of an accurate result, since, as George pointed out, the possibility of inter-
ference due to phosphates, silicates and free mineral acid is everpresent.