This question was recently emailed to us by a member:

I have a 4.5 acre lake (average depth 10') that has really muddy water that I need to clear up.  Can you help?  What do I need, where can I get it, and who can do that sort of thing?  Where can I get bulk gypsum (calcium sulfate) for the Emory, Texas area?  That's in NE Texas.

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Mr. Mullin

The two chemicals primarily used to clear muddy pond water are Alum (Aluminum sulfate) and gypsum (calcium sulfate).  Alum is the most effective product but should not be used in ponds with low alkalinity levels (less than 20mg/L as CaCO3) without the use of hydrated lime (1/2 part lime for 1 part Alum) or it may cause pH levels to drop, negatively affecting fish growth or survival.   The chemical should be mixed to form a solution of 10 parts water to 1 part alum and added directly to the water by pouring it into the wake behind the prop of a boat. 

Gypsum is not as effective as Alum but can be used to control turbidity without lowering Alkalinity or pH levels.  Gypsum must be added to achieve a concentration of 100 to 300 mg/L for effective turbidity control.  In hard-water ponds (calcium hardness greater than 50 mg/L), the water is nearly saturated with calcium and gypsum may be ineffective.  In that situation, alum will be the only effective coagulant.

There is a test called the bucket test that can be used to determine how much Alum or Gypsum should be applied to a pond based on water turbidity:

Obtain a small sample of a selected coagulant (alum or gypsum).  Collect four 5-gallon buckets of turbid pond water. Carefully weigh four separate, small quantities of alum: 0.2, 0.3, 0.4 and 0.5 g.  Add each weighed amount of coagulant to one bucket of water and stir vigorously for 1 to 2 minutes.  Then, stir briefly every 5 minutes for up to 30 minutes.  Observe the clarity of the water.  Select the minimum dose of coagulant that clears the water. For example, suppose the water cleared in buckets 3 and 4, but did not clear in buckets 1 and 2. The dose of alum added to bucket 3 (0.4 g) would be the proper one.  (If using gypsum simply multiply the amount of coagulant added to each bucket by 10, adding 2, 3, 4 or 5 g gypsum to each bucket.)

 Many companies that carry industrial chemicals sell Alum and/ or gypsum.  As for a specific place in that area I am not sure, but gypsum can be ordered from a company called CL ranch at http://www.naturalgypsum.com/catalog.html.

I hope this information helps.  We offer consulting and management services on a time and material basis.  If you are interested or have any other questions please let us know.

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