Yep. If those viewing this thread want to get a nerdily-accurate alkalinity value for their tank water, Randy has published a DIY alkalinity assay
based on pH measurement and a standard acid titrant.
I've mentioned this before, but I'll add a bit to Randy's excellent article. What he's explaining in the article is the standard method for doing acid/base titration - in this case, the base is the aquarium water. Or more specifically, the carbonate/bicarbonate in the aquarium water and a few other anions that are present in low amounts and don't make a difference for a reefer's purpose. The acid is the titrant - you could use any acid (well, most of them anyway) as long as it has a known normality/molarity, but most often hydrochloric acid is used in a lab, and is readily available to reefers from on-line sources.
What I've mentioned is that there are some standard laboratory equipment items (in addition to the pH meter that Randy notes in the article) that makes performing the procedure that Randy's outlined in the article a bit more convenient. Specifically, you'd like to have a piece of glassware called a burette, a laboratory stand and holder for the burette, a magnetic stir plate, and a magnetic stir bar. The burette provides an accurate and convenient way of measuring the total amount of standard acid that you've added drop-by-drop to the sample to get the pH down to about 4.5, and the magnetic stir plate and bar keeps your sample thoroughly mixed as you add the acid.
The burette, ring stand, burette holder, magnetic stir plate and stir bar are much, much cheaper than they were just 15-20 years ago, and you can easily buy them off of
Amazon. If you decide to go this route, note that burettes come in different liquid capacities. In Randy's article, he notes that if you use 0.1 N HCl, your aquarium water has an alkalinity of 7 dKH, and you use a tank water sample size of 250 mL, you'd need 6.25 mL of 0.1 N HCl to complete the titration. For this particular example, you'd like to have a 10 mL burette, since you'd like to use at least 1/2 of the total capacity or more of the burette during your titration for the best accuracy of reading off how much acid titrant you used. Generally, glass burettes come in standard capacities - e.g., 1 mL, 5 mL, 10 mL, 25 mL, etc... Presuming that you use Randy's recommended 0.1 N HCL titrant, and use a reasonable water sample from your aquarium (i.e., 250 mL), the 10 mL burette size will be the most useful. However, if you use a larger volume of sample, the 25 mL burette size may be more appropriate, while if you use a smaller size sample such as 50 mL, the 5 mL burette size may be more convenient.
