alk test kit article?

[piercho]

I think you once wrote an article that included the use of alkalinity test kits. I'd like to know if I can verify the accuracy of a test kit. Anyway, I can't find the article (if it exists) TIA.

[Randy Holmes-Farley]

There are two ways that I can think to test a test kit. One is to make a standard solution containing something like baking soda, and the other is to test some tank water, and then do a pH titration on the same water.

For the former, you'll need an accurate balance to weigh out baking soda. For the latter, you'll need a pH meter and an acid standard.

[piercho]

Hmmm, OK let me try the subjective approach...
I've been using the same bottle of reagent to titrate alkalinity for going on 10 months. When that bottle finally ran out, I got a new bottle (of the same brand reagent), and with the new bottle my TA measures higher - by a lot. My last measurement with the old bottle was 3.0-3.5. The first measurement with the new bottle was 5.0+, and that measurement was made immediately after the last measurement with the old bottle. I'm using all the same test containers. Both bottles produced consistent results. This type reagent tritrates from blue to yellow-green.

My rationalization is that I was careless keeping the old bottle tightly sealed and some water evaporated off, concentrating the reagent. I would hope that 2 lots of the same brand reagent (fasTest) would not vary by so much.

Sorry to bug you. The reasonable solution is to buy a second brand kit and compare the results. Anyway, is my water-evaporation theory likely? Do reagents need to be used up within a few months as a general practice?

[Habib]

Howard,

My rationalization is that I was careless keeping the old bottle tightly sealed and some water evaporated off, concentrating the reagent.

If Total Alkalinity has remained the same then something like 30% of the water should have evaporated. This is IMO very unlikely especially if the cap was in place although perhaps not tightly sealed.

The reasonable solution is to buy a second brand kit and compare the results.

I don't know if in the USA watersupply companies are willing to give current total alkalinity values and if they are always honest in that matter. But if so then you could test the tap water with your total alkalinity test and see what results you get.

In case tapwater TA is low then you can use as far as I know double the amount of water with titrating type of total alkalinity test kits. In that case multiply the value given by the watersupply company by 2.

It is also good to know when the watersupply company gives the values which units are used e.g. meq/L (milli-equivalents per liter)

[Randy Holmes-Farley]

Howard:

The problem could be as simple as quality control by the manufacturer, or something more complicated, such as a water parameter change in you tank. As you suggested, a new kit from a new manufacturer is likely the easiest way to go. If it matches the existing kit, then you haven't wasted any money as you can use them both until they run out.