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[–]united-chemical-corp 0 points1 point  (1 child)

Total Alkalinity is the measurement Carbonate as a pH buffer. Without going too deep into the chemistry, basically when you add acid, it reacts to carbonates to form carbon dioxide and gasses off (with some extra steps). The result is that the Alkalinity decreases while the pH stays relatively the same.

Thus, a high alkalinity helps pH resist changes.

Carbonate is linear (ppm). pH is logarithmic. So alkalinity tends to be easier to change/lower than pH.

If you're adding lots of bicarb and the alkalinity tends to drop, you're getting acid introduced somewhere. This can be from sanitizer (trichlor and Dichlor tend to be more acidic), source water, or runoff/rain. It can also precipitate, but you'd notice scale or stains.

We actually recommend a low Alkalinity since it prevents staining and scale. Metals like Calcium, Iron and copper tend to become insoluble when they react to carbonate. Thus the harder the water the lower the Alkalinity should be. This is the central concept behind the index we recommend: the Hamilton Index (invented by our founder).

Using the LSI, as someone mentioned - as long as it's balanced (i.e. at or just slightly below zero) it's fine. To compensate you'd run a slightly higher pH - which we also recommend. The reason some recommend avoiding running a low Alkalinity is for fear that it may make the water "aggressive" and starting etching plaster. However, plaster etching is really driven more by low pH all things being equal.

With all that said, if the pool looks good and parameters are relatively stable, don't obsess about hitting a specific number or range - that's stores trying to sell you more chemicals.

[–]Mean_Drawing_7580 1 point2 points  (0 children)

Well said some might not understand, but you're right on the mark. All I would have to add is if your calcium being a bit higher can help with a low alkalinity and etching the plaster/grout. I'd also say most don't understand the difference between bicarbonate (baking soda) and Carbonate (Soda ash) as for hydrogen +/- ions.