Mackey,
I am going to copy Larry Laitner's paper on muriate of potash here for you:
"Managing Nutrients to Control Algae
by Larry Laitner
llaitner@rocketmail.com Solving the algae problem in a pond is not exactly rocket science but
it involves several factors that must be understood in an integrated
manner. Actually it is just basic agricultural science. Put as simply
as possible the problem is phosphorous. Those of us that have been
paying attention to environmental rhetoric know that phosphorous
that gets into our streams, rivers, and lakes causes water quality to
deteriorate. The same is true of small artificial aquatic systems
except that the phosphorous doesn't come from external sources, it
comes from the fish themselves. The problem is that small artificial
ponds do not have the same range of inputs and outputs so that the
phosphorous fish produce can accumulate in the system. When the
phosphorous content becomes high enough planktonic algae grows
rapidly and the water turns green. It will stay green until the
phosphorous content of the water decreases.
A pond system that can tie up dissolved phosphorous as quickly as
the fish produce it will be clear or nearly so. The key to removing
dissolved phosphorous from the water is to have vigorous growth of
vascular plants. Water hyacinths are among the best choices for this
task. The catch phrase here is "vigorous growth," since it is quite
possible to have lots of hyacinths in a pond and still have algae.
What happens here is that the hyacinths do not have all the other
nutrients to support growth, so that the phosphorous will not be
removed. In this case the hyacinths will do poorly and the planktonic
algae will thrive.
So what nutrients do the hyacinths need to have vigorous growth?
Ok, here's the agricultural science part. The three main nutrients are
nitrogen, phosphorous, and potash. If any one of these is missing the
hyacinths will not grow. There are also some micro-nutrients that
we will ignore for now. Nitrogen and phosphorous are produced by
fish and we can safely assume that any pond that has fish will have a
continuous supply of these nutrients. The source of these nutrients is
the food that the fish eat and excrete as waste products. Potash,
which we also know as potassium, can come from the mineral
content of water that flows onto natural bodies of water.
Unfortunately, potash is often deficient in artificial ponds. If potash
is deficient, vascular plants will not grow well and thus will be
unable to utilize the phosphorous and nitrogen. When this happens
planktonic algae will bloom and your pond will look like pea soup..
What usually happens in an artificial pond is vascular plants will
grow until one of the three nutrients is exhausted. The other two
nutrients will remain in solution, unusable until the missing nutrient
is replenished. Then growth will proceed slowly at a rate that is
controlled by the rate that the missing nutrient is produced. The key
to clear water is to make sure that the nutrient that runs out first is
phosphorous. Once this state is achieved the phosphorous the fish
produce will be utilized almost immediately by the plants that are
awaiting its production.
Now the task is to manage the nutrient load in the water so that
nitrogen and potash are always available. Nitrogen might be
deficient in a pond that has no fish but will normally be plentiful if
fish are present. Potash must usually be added to ponds, sometimes
in substantial quantities. A pond that has had an ongoing "green
water problem" may accumulate a substantial burden of phosphorous
over time. When this occurs any added potash will be quickly used
by the plants that have been starving for it for some time, so several
additions of potash will have to be made over a period of time.
How much potash should be added? How often? Tetra Pond makes a
product called Flora Fin that is a very expensive 6% potash
solution. They recommend initially adding 165ml of this solution to
800 gallons of water followed by one half this amount every two
weeks. My experience is that this amount is often not enough,
especially if the initial load of phosphorous is substantial. I would
recommend this full dose at least once a week until the water clears.
A very cheap potash solution can be made from muriate of potash
(potassium chloride - KCl), which is available at any garden supply.
Add 50 grams of muriate of potash to 500 ml of water to create a
6% potash solution at a cost of about ten cents, or you can just buy
Flora Fin for about ten dollars a bottle. (Buy several, it doesn't go
far)
At the beginning of this discussion I said we would ignore
micro-nutrients but it is possible that one of these may also be
lacking. The micro-nutrient most likely to be lacking is iron. One
way to supplement iron, and the other micros as well, is to add a
very small quantity of Ironite. Ironite is intended as a lawn fertilizer
so it comes in a big bag that will last several lifetimes. It also
contains nitrogen in the form of urea which is toxic to fish if you add
too much, so go easy. Be particularly cautious with this if your pond
hasn't been in operation long enough to have colonies of the various
de-nitrifying bacteria that turn urea into the relatively harmless
nitrates that your plants will consume. If you are not sure about this
you can test your water for ammonia.
If you are successful in managing your nutrients your water will be
clear, the plants will be a lush dark green color, and hyacinths will
develop long root structures as they attempt to collect the
phosphorous as quickly as it is produced. As winter approaches try
to leave the hyacinths in the pond as long as you can so the
inevitable winter phosphorous build-up will be minimal. During the
winter continue to add your potash solution once a month or so as
long as your pond isn't frozen over. During the winter you will
probably have some filament type of algae grow on the sides of the
pond as the various nutrient processes continue at reduced pace. The
filament algae will tie up phosphorous at least temporarily (until the
fish eat it) but that will suffice since fish do not excrete much
phosphorous in the winter. In the spring get the hyacinths in the pond
as early as frost allows and boost the potash again at that time.
It is imperative that the hyacinths be removed from the system either
when the frost comes if you live in an area where winter conditions
occur or on an ongoing basis in frost free areas. The hyacinths tie up
the phosphorous; only you can remove it. If you leave the hyacinths
to rot, the phosphorous will be returned to the water.
Your fish probably don't care much about the color of the water but
most humans like the water clear so they can see the fish. If you
manage your pond's nutrients you should have clear water most of
the year with only a slight murkiness in the spring during the time
between the awakening of fish metabolism and the arrival of your
hyacinths."
Mackey, in June of 2001 the following recipe was posted on Garden Web:
2-3 Tablespoons of potash to 1 pint of water. Then 1/8 cup of that mixture per 100
gal. of pond water per week. One cup of mixture treats 800 gal......1 pint of mixture
treats 1600 gal.....etc., etc.
The only caution would be that muriate of potash contains 40 to 60 percent chlorine, and some ponders use as little as they can to get the desired result. Others throw a cupfull into the biofilter of a 2,000 gallon pond because they are convinced that the chlorine is not "free chlorine" and thus will not hurt the fish. I use
5 tablespoons in my 2,700 gallon pond, but only twice durnig the summer. I put it in one tablespoon a day for five days, rather than dumping all of it in at once. It is always best to make environmental changes slowly where fish are concerned.
