Egyptian hieroglyphics dating back to 1500 B.C. made reference to an additive that was used to set dye in material and cure leathers, but which also would cause suspended particles in water to settle out. Similar documentation came from the Romans in that same time frame mentioning an additive that was used to make bitter water potable, though the compound was not referred to by name.

It wasn’t until 77 A.D. that Pliny the Elder (23-79 A.D.) gave the name “alumen” to this compound of aluminum and sulphur and to its use as a method of coagulation in his work Historica Naturalis (Natural History). First century Greek writings document the mining and distribution of alum, as well as the use of aluminous earth as a precipitant in water. In that same century, the practice of using Ming Fan (alum) in traditional Chinese medicine grew in popularity, as did the practice of adding the product into tubs to clarify water. By the mid-1700s, aluminum sulfate was being used as a water treatment at municipalities throughout much of England.

Today, alum is used worldwide for lake and pond treatment, as a blood coagulant in hospitals, as a soil additive, in paper production, in fertilizers, soaps, greases, drugs, cosmetics, sewage and wastewater treatment. Aluminum sulfate still is used as one of the essential treatments in drinking water, remaining as one of the first processes a municipality uses as the water is retrieved from a reservoir.

Alum remains popular in water treatment not only because of its ability to clarify potable water, but also due to its success in lowering levels of arsenic, phosphates, pathogens (including giardia and cryptosporidium), viruses and disinfection byproduct precursors.
Alum also was widely used in the swimming pool industry as both an additive to sand filters and as a coagulant until about 30 years ago, when man-made liquid polymer clarifiers began to increase in popularity.

Slowly the 3,500-year-old water treatment began to disappear from the shelves of pool stores and distribution warehouses.

The new liquid clarifiers were easier to use, while alum was perceived as overkill in hazy water situations — and by comparison, it was. As an additive to sand filters, it was considered by many to be problematic. In our industry, the extinction of this product was prevented by one simple fact: Liquid clarifiers could not do what alum could do in a worst-case scenario, in an extremely turbid (or swamp-like) water situation. This left the modern pool guy with only one option: drain and refill.

Aluminum sulfate is both pH- and temperature-dependent. (The use of alum will be more successful in water temperatures above 70 degrees; the warmer the water, the better.) To use this additive effectively, first you must adjust the pH to 6.5 to 7.0. The closer the pH is to 7.8, the more unstable the alum will become. As pH gets closer to 6.0, the possibility increases that the alum will dissolve.

Next, if the system has a sand or DE filter, manipulate the valve to the recirculate position so water can bypass the filter. In the case of cartridge filters, remove the cartridge and reassemble the filter without the element.

Brush the pool walls to free any debris or algae. Broadcast aluminum sulfate at a rate of 4- to 6 pounds per 10,000 gallons across the pool surface. Set the time clock for the filter so that the system will run for two hours. This allows enough time for the alum to distribute. Then turn to off. Remove the “On” tripper from the time clock so the system does not start again until you manually turn it on.

Wait 12 hours — at this point the pool should be fairly clear, with a thick layer of sludge on the pool floor. Vacuum to waste, but do this extremely slowly so as to not stir what has settled. Top off the pool due to water lost from vacuuming. Place the multiport valve back into the filter position, or replace the cartridge filter element. Balance the pool water.

Note that this process will work best in a pool that does not have a lot of heavy debris — leaves, twigs, etc. — on the pool floor, due to the required vacuum process.

Aluminum sulfate works by destabilization of colloidal particles. The formation of metallic hydroxide causes the debris to settle at the pool bottom.

The substance is relatively inexpensive, averaging between $0.45 and $0.65 per pound when purchased in bulk sizes of 50 pound bags. But due to the drastic decline in popularity over the last three decades, this product isn’t always instantly accessible, so you most likely will have to order in advance through your local swimming pool distributor.

With the large number of real-estate owned homes and foreclosures in the market, the ability to take a body of water that has gone untouched for years and make it swimmable in 24 hours — without the additional cost of water — may give a service company an advantage over the competition.

Above and beyond the concern of the cost of water, consider our many areas of the country that still face water restrictions. Simply draining and refilling may not be an option. Perhaps a more conservation-minded solution to the current problem lies in a 3,500-year-old means of clarifying water.

Water covers approximately 70 percent of the Earth’s surface, but less than 1 percent is available for human use. The world must share this small amount for agricultural, domestic, commercial, industrial, and environmental needs. Across the globe, water consumption has tripled in the last 50 years. Managing the supply and availability of water is one of the most critical natural resource issues facing the United States and the world, as identified by the U.S. Environmental Protection Agency.