Pond Boss Forums GENERAL QUESTIONS Water chemistry What do these numbers mean to my pond???

Just a quicky on the total alkalinity and total hardness. Typically these are reported in mg/L equivalent calcium carbonate. I am assuming that this is how these number are reported.

Total alkalinity, by textbook definition is the total titratable bases in the pond. There is no real alkalinity that is in a pond, it is rather an index. There are two main reasons to have alkalinity in ponds, the first is to provide a source of carbon for primary productivity. This is much less of importance than the pH buffering capacity of the water which is the second. If you have no alkalinity in the water the pH can undergo dramatic swings from day to night. Phytoplankton will consume CO2 (acid) during the day and produce O2. During the daylight hours, also, there is production of CO2 and consumption of O2 by bacteria decomposing organic matter. So the result in the day time considering photosynthesis will be greater than respiration by bacteria is that CO2 is used up. That means an acid is taken out of the water. The pH will then rise. At night however there is no photosynthesis, but respiration still occurs not only by the bacteria, but also by the plants which were conducting photosynthesis in the daytime. The result is acid is put back in to the water and the pH will decrease. Now the alaklinity. The alkalinity will tell you how much capacity your pond has to buffer against wide swings in pH. Generally, waters can be up to 200 mg/L total alkalinity and even higher and cause no problem so too much is not really a bad thing. Too little, however, can result in the large pH swings. I would apply lime to get the total alkalinity up to at least 30 mg/L in a sportfish pond. I would suggest higher for a aquaculture pond. The total hardness is the sum of the divalent cations in solution. This basically means the amount of calcium and magnesium. This is important they are essential plant and animal nutrients, but there is an indirect effect on pH also. In order for the total alkalinity to buffer against the highest pHs you need to have calcium. As bases increase in the pond the buffering capacity of alkalinity will cause calcium carbonate to precipitate (form a solid) and sink to the bottom of the pond. If there is no calcium in the pond, high pHs might be a problem. Although many natural ponds don't exhibit this high of pH. Magnesium behaves similarly to calcium, except calcium carbonate will precipitate before magnesium carbonate.

Another benefit of adding calcium carbonate (limestone) to your pond is that in recently excavated ponds there may be some acidity in the soil that the limestone can neutralize.

While you may not need fertilizer, you may want to think about lime. Studies have shown that there is a dramatic difference in pond primary productivity when the total alkalinity is above 20 mg/L.

Good luck, sounds like your pond is in pretty good shape