TGW - facts are critical to any understanding especially complicated ones like pond chemistry. There is an excellent article by Dr. Boyd in the recent PB mag - please read it. It is best to go slow on pond chemistry/productivity issues unless the problem issue is at the critical (low DO < 5 and dropping for example) stage. It is common in ponds with a limiting factor (low alkalinity , low N or low P) when augmented (lime or fertilizer) to grow like crazy. That is not a good thing and can cause problems like you described especially if other factors are involved.

What can you provide us as to alkalinity , hardness and N & P. Any info on well water. I have found that while nudging mother nature can give excellent results , total war against her is futile. One of the comments above is about large scale changes in pond chemistry. A prolonged fight between you and your dirt and water (pond chemistry) could be a wreck. You need facts first and you may have them. Here is but one example dealing with many southern ponds from the quoted Fact Sheet. Note the differences with respect to groundwater (well).

Problems with high pH seem to occur most often in ponds where total alkalinity (the amount of bicarbonate and carbonate in the water) far exceeds water hardness (the amount of calcium and magnesium in the water). For example, it is common for freshwater prawn ponds at the Mississippi State University aquaculture unit in Starkville to have high pH in late spring. The groundwater supply for these ponds has a hardness of about 30 mg/L as CaCO3 and an alkalinity of about 90 mg/L. An even wider disparity between hardness and alkalinity is found in many other waters, particularly those in the southeastern coastal plains where many groundwaters have alkalinities exceeding 150 mg/L and hardness values of less than 10 mg/L.
Deficiencies in hardness relative to alkalinity can be corrected by adding gypsum (calcium sulfate). The effectiveness of gypsum treatment in reducing pH is subject to debate; at best, it is a preventive procedure rather than an emergency treatment. Hardness deficiencies should, therefore, be corrected before stocking, preferably as soon as the pond is filled in the spring.
The amount of gypsum needed to roughly balance hardness and alkalinity can be calculated by subtracting hardness from alkalinity and multiplying that value by two. For example, if hardness is 30 mg/L as CaCO3 and alkalinity is 90 mg/L as CaCO3, then 120 mg/L of gypsum will be needed. This would require about 2,500 pounds of gypsum in a 2-acre pond that is 4 feet deep. This is a large amount of gypsum, but the results of treatment should be long-lasting because calcium is lost from ponds only when waters are diluted by excessive rainfall or by the addition of water with a low calcium content.

From another Fact Sheet - Agricultural limestone can be used
to increase calcium concentrations
(and carbonate-bicarbonate alkalinity)
in areas with acid waters or
soils. However, at a pH of 8.3 or
greater, agricultural limestone will
not dissolve. I would be surprised if ag lime caused your water to go to 8.5.

Last edited by ewest; 12/12/17 11:12 AM.