Pond Boss Forums GENERAL QUESTIONS Water chemistry Alkalinity Test Kit Verification

There have been a few questions by pond owners who had problems determining if their alkalinity test kits were working properly. Bill Cody and I worked up a basic "at home" recipe for those who wanted to check their kits to make sure the chemical reagents were still effective. An initial warning, alkalinities measured from this solution will vary depending on the accuracy of measurements made throughout the entire procedure. Most economical alkalinity kits themselves are not exceptionally accurate or precise either. Therefore, use of this inexpensive method should be limited to determining if the test kit works (or if it is being used properly) and should NOT be used as any sort of standard for calibration!

Since alkalinity is basically a measure of the dissolved carbonates, sodium bicarbonate (Baking Soda) can be used to produce a solution of a known concentration. This solution can then be tested with your alkalinity kit to determine if it is operating properly. Two separate solutions will have to be made to measure out the baking soda with common household items.

First, carefully measure out 1 quart of DISTILLED water in a mason jar or similar container. It is critical that you use DISTILLED water, as the alkalinities will be elevated if tap water is used. To this quart of distilled water, add 1/4 LEVEL teaspoon of Arm and Hammer Baking Soda. (We found that different brands of baking soda will produce slightly different readings.) By 1/4 teaspoon I do not mean taking a spoon from the drawer and filling it about a quarter of the way full. You will need an actual 1/4 teaspoon measuring spoon and will need to scrape the baking soda LEVEL in the spoon. Add this 1/4 teaspoon to the quart of distilled water and mix for 10-15 seconds.

Once the above solution is well mixed, use a 1 teaspoon measure to place 2 teaspooons of the above solution into a small measuring cup. After you have added the 2 teaspoons of solution, fill the measuring cup to the 1/2 cup markwith DISTILLED water. Be careful to make sure that the surface line (meniscus) is on the 1/2 cup marking. Mix this second solution thoroughly. This second solution can then be tested according to the instructions with your alkalinity test kit.

Bill and I tested four replicates of this procedure using the same methods with the average result being 64 mg/l of calcium carbonate. Our results ranged from 62 to 68 mg/l using a Hach Alkalinity Digital Titration method. The actual result you obtain from this will vary depending on the accuracy of the measuring utensils you are using, brand of baking soda, as well as accuracy of your particular test kit. If care is taken in preparing the solutions, I would anticipate that most test kits will give results between 45 and 80 mg/l (ppm) calcium carbonate for the solution. Once again, this is not intended to be a laboratory standard, it is just a rough estimate for you to make sure that your test kit works or that you are testing correctly. If you have a more sophisticated alkalinity test kit and want to compare the accuracy of your test kit, I would recommend buying an actual alkalinity standard solution. These are available from Hach Company and other laboratory suppliers.

Recipe Summary:
1/4 teaspoon baking soda in 1 quart DISTILLED water.
Put 2 teaspoons of above solution in a SMALL measuring cup.
Add enough distilled water to make 1/2 cup.
Use this solution to test for alkalinity.

Alkalinity results should be between 45 and 80 ppm; closer to 64 the better.

Hope this helps out. If you try testing this standard solution we would be interested in your results. Keep in mind that most basic test kits that use the "large drop method" will only provide ball park - close to results.

Jason and Bill
Thought I'd try your test out. Only problem was I didn't have any distilled water on hand yet and since I am on well water with reverse osmosis's system thought I'll give it a try till I get some distilled water. Test kit is a (cole-parmer total alkalinity k-9810)I've had this kit about 1 and 1/2 years now. Did the test to the exact measurements you stated. On this test kit range is 10-100ppm only problem is that it numbers only shows 50 to 70 and then 70-100 but did 3 different vials and each time was right in the middle of the 50-70 mark. Great test, was always wondering how long test kit was good for.
P.S I have a kenetico reverse osmosis system and should this still have worked ok. THANKS PO

PO - We are glad it worked out fairly good. A person in our situation is exactly who we worked up this simple alkalinity standard for.

Water produced by reverse osmosis (RO) essentially has no alkalanity or hardness. For all practical purposes RO water is just about as pure as distilled. HOWEVER as the RO membrane ages and collects contaminants the resultant water does contain some impurities. Thus the RO membrane element should be routinely changed. The local company (Culligan) that I buy my filters from recommends a change of the RO membrane every 5 to 7 yrs and carbon element every year, depending on the amount of inflow, usage by the membrane, AND the quality of incoming water (amount of contaminants & dissolved solids). Larger households than two people my need to replace membranes sooner than every 5 yrs. Water company said that they can check a small sample of the RO water and tell when the RO membrane needs replacing. They probably do a conducivity test.

Bill I change the yarn filter every 6 months and the carbon element every June, and it is always as clean as when I installed it 6 months earlier.Maybe because I have a whole house yarn filter before my water softner too. Kenetico people never told me when I bought the unit that I had to change the RO membrane. I'll call them tommorow. Thanks I'm always learning on this site.

Gentlemen: Thanks for this information..exactly what I was looking for. I will be doing this in the not too distant future and some of the other suggestions from another thread.

Jason and Bill, Thanks.

PO I have the same test kit and I am unable to get a reading.On the direction I received it is unable to give accurate readings, it will not turn red to bright green. Am I doing something wrong or is my total alkalinity so high it is unreadable? If so what is that the indication that I should be doing? thanks