I want to clarify and elaborate on Bob's previous commment. The part of his post I am emphasizing is below:
Hydrated lime is Calcium hydroxide. Its pH is way too high, somewhere around 13. It is volatile, and artificially raises the pH. That's not the problem in ponds. Alkalinity is the problem. Hydrated lime cannot raise the alkalinity. Alkalinity is a measure of carbonates.
For this information I had to go "to the book" and I used my textbook for a graduate school water chemistry course - Chemistry For Sanitary Engineers by Sawyer & McCarty - McGraw-Hill Series.
I propose that hydroxides do contribute to alkalinity of a pond. My reasoning follows:
The book states -"Although many materials may contribute to the alkalinity of a water, the major portion of the alkalinity in natural waters is caused by three major classes of materials which may be ranked in order of their association with high pH values as follows: 1) hydroxide, 2) carbonates, and 3) bicarbonates. For most paractical purposes, alkalinity due to other materials in natural waters is insignificant and may be ignored." "Under certain conditions natural waters may contain appreciable amounts of carbonate and hydroxide alkalinity. This condition is particularly true in surface waters where algae are flourishing." "The algae remove carbon dioxide, free and combined, from the water to such an extent that pH values of 9 to 10 are often obtained."
"...... alkalinity is thus a measure of the buffer capacity.... . Alkalinity is measured volumetrically by titration ..... . The amount of acid required to react with the hydroxide, carbonate and bicarbonate represents the
total alkalinity." If necessary the hydroxide, carbonate and bicarbonate alkalinities can be calculated.
As an interesting side note, the removal of carbon dioxide by algae tends to cause a shift in the forms of alkalinity present from bicarbonate to carbonate and from carbonate to hydroxide. During these changes the
total alkalinity will REMAIN CONSTANT.
This is interesting stuff if you are concerned with the details of alkalinity.
