Pond Boss Forums INTRO Questions & Observations Odd gypsum experience

I have recently had some turbidity problems with my pond and embarked on the gypsum slurry test described on the Texas A&M website under "Clearing Muddy Ponds". Not having any gypsum handy I went to the neighborhood feed and seed store and bought a 50# sack of pelletized agricultural gypsum. When I made my slurry with 2 tbs of gypsum in a gallon of water it turned cloudier than my pond water by a huge amount. This happened with purified water! Some of the turbidity settled overnight but most stayed. When I used it as a slurry I could not get any clearing of the pond water at any concentration.
I then tried aluminum sulfate which worked like a charm. I assume the turbidity from the gypsum was due to a binding agent used to pelletize gypsum dust but am at a loss to understand why no amount of gypsum I added would clear my water. The only difference between aluminum and calcium is the valence of +3(alum) and +2(calcium). Is there some chemical explanation like the different dissociation constants of the two elements?

What about this Layton .

http://srac.tamu.edu/index.cfm?catid=25
SRAC 460 Control of Clay Turbidity in Ponds

Although not nearly as effective
as alum, gypsum also can be used
to control turbidity but without
the loss of alkalinity. Gypsum
must be added to achieve a concentration
of 100 to 300 mg/L for
effective turbidity control. For
most ponds, gypsum application
rates will range from about 1,000
to 2,000 pounds per acre (Fig. 4).

"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."

All the coagulants mentioned can
remove phosphorus from water.
As phosphorus is an essential
plant nutrient, it may be necessary
to fertilize the pond after treating
it for turbidity. On occasion, phytoplankton
and clay can mutually
coagulate, so fertilizing to start a
phytoplankton bloom may also
clear water of suspended clay particles.
Organic matter such as chopped
hay or cottonseed meal can reduce
clay turbidity in farm ponds.
However, large amounts of material
must be added to the pond,
which may deplete the dissolved
oxygen as the organic matter
decomposes. It may also be difficult
and costly to transport and
uniformly distribute large
amounts of organic matter.

Alum
makes water more acidic. In
ponds with low alkalinity (less
than 20 mg/L as CaCO3) it can
reduce water pH to levels that
may affect fish growth and survival.
In low alkalinity ponds, add
1/2 part hydrated lime for every
part of alum applied in order to
maintain proper pH.

Layton, contact US Gypsum. I did last Spring and they were extremely helpful.

Not sure I understand your post regarding use of purified water instead of pond water.

Dave, I used purified water to make my slurry to add to the pond water. Therefore, there was nothing to react with the gypsum and make it murky other than the gypsum itself. It got so murky you could not see through a drinking glass of the stuff, and it did not settle, the slurry alone, that is.
Ewest, thanks for that post. You fill the role of the website reference librarian beautifully. I suspect the calcium saturation is the answer. I have used gypsum in the past successfully and so I was puzzled by it not clearing my water in the test. My new theory is that, due to drought conditions here in Oklahoma, there has been concentration of the normal calcium in the water to the saturation point alluded to in Ewest's post. I have been able to keep my water levels
semirespectable in my 2 1/2 acre pond with my pump
but the well water is loaded with calcium.