GYPSUM
(CaSO4)
Gypsum, as calcium sulfate is commonly known, is an invaluable material for watergarden use. It is a common mineral, with many uses, from being a major component in home and building construction to food additive (http://www.minerals.net/mineral/sulfates/gypsum/gypsum.htm and http://www.dietriot.com/fff/mcd/mcd.html ).
Calcium sulfate is particularly useful in the watergarden because of its water clarification properties. As an electrolyte, calcium sulfate is useful in maintaining fish health, and is a listed ingredient in the product "POND SALT" sold by Aquarium Pharmaceuticals (http://www.aquariumpharm.com/ ). Calcium sufate is used in municipal water supply treatment plants for water clarification, and has been proposed as a replacement for aluminum sulfate for this purpose because of concern over human consumption of aluminum (http://www.hc-sc.gc.ca/ewh-semt/water-eau/drink-potab/aluminum-aluminium_e.html).
It is helpful for calcium sulfate to be dissolved before adding to your pond, in order to avoid clogging your fishes gills with the particles. For this reason, you should mix the gypsum with water, creating a slurry before adding to your biofilter. Rates of calcium sulfate application vary with water turbidity and PH. Don Steinback and Billy Higginbotham offer a method for determination of application rates based on test samples of water clearing rates. (http://agfacts.tamu.edu/D11/Calhoun/Mar/Recfish/Pondmgt/mudpond.htm>)
Their chart applies to farm ponds and is presented in pounds of gypsum per foot-acre of pond. Their method is mix two level tablespoons of gypsum in 1 gallon of water, stirring until the gypsum is in a slurry. Then in 1 gallon glass jugs, collect several samples of the pond water to be tested. Then add the slurry to the sample jars at various rates (Number of tablespoons ) and record how many tablespoons of the slurry you placed in each jug on the jug. After 12 hours, the jug with the least number of tablespoons of slurry that has cleared will tell you how much gypsum to add to your pond. I have converted their chart to home watergarden use as follows:
Gypsum Application chart per 1,000 gallons of pool water
