of water usage and water balance chemicals that may be needed.
One of the other ways to keep CYA levels managed is to reduce the use of trichlor tablets and use liquid chlorine to shock or switch to either liquid or cal-hypo as the primary source of sanitizer. Neither liquid chlorine nor cal-hypo contain CYA, so you can set your CYA at 30-50 ppm and forget it. Keep in mind that cal-hypo contributes calcium as a byproduct, and every pound of calhypo raises the hardness by 8 ppm. Liquid chlorine leaves behind sodium chloride as a byproduct, and while this does contribute to the total dissolved solids (TDS), compared to high CYA or calcium levels, it has the least detrimental effect.
There are other ways to lower CYA. There are commercially available products that use a microorganism to break down the CYA. These can be effective, but they are costly, and they must be used precisely according to instructions or they will not work. For example, the water must be warm — not much less than 70 degrees. Also, because the product uses beneficial bacteria, the chlorine level must be low — usually no more than 1 ppm. It may not be recommended to lower the chlorine in the summer when it is hot and sunny. It may be better to try these types of removers in the off-season, but keep in mind that the water needs to be near 70 degrees.
One recent anecdotal method for the removal of CYA has been the use of alum. This is basically a coagulation method where the aluminum sulfate grabs the CYA into a floc, which settles to the bottom of the pool. Alum has been used in water treatment for centuries, and it is used in lake treatment for the removal of phosphates in the same way. Rudy Stankowitz from Florida was among the first service techs to promote the use of alum to other service pros. His podcast and publications are probably the best source for techniques on using alum to remove CYA. Like the biomethods discussed above, preparation is important, and the water again must be around 70 degrees. The pH should be lowered to 7.0 if possible because alum flocs faster at a low pH. Total alkalinity and calcium hardness must be in recommended target ranges. The filters must be bypassed, so set sand filters at “recirculate,” and remove cartridges from cartridge filters. The process takes 8.33 lbs. of alum per 10,000 gallons of pool water, which is circulated for 2 hours. Next, shut off the pumps for 12 hours to allow the floc to settle. The floc is then vacuumed slowly to waste.
Some claim a 20-to-30% drop in CYA after dosing with alum. Keep in mind that if you have very high levels of CYA, this method may be tedious and time consuming. For example, if you had 200 ppm of CYA, a 20% reduction would result in 160 ppm. Unless you really overloaded on alum or did the treatment several times to get to 50 ppm, this would not be helpful in managing your free chlorine. If your goal is to achieve a free chlorine concentration that is 7.5% of the CYA, bringing the CYA down to 160 ppm would still require 12 ppm free chlorine to keep the pool clear. The alum method could be useful in times when draining is restricted. However, proactive drain and dilution is still the most effective and economical way to lower CYA.
If you use trichlor tablets or dichlor at all, you should be doing regular CYA testing at least once a month. The dilution turbidity test method is one of the best and most accurate methods. There are test strips as well, but they are not as accurate as a turbidity test. When you test for CYA, the pH should be 7.4-7.6, ideally 7.5. Water temperature will affect the accuracy of the test. High temperature (90 degrees or more) will produce a false low reading of 15 ppm or more. Cold water of 60 degrees or less will give a false high reading by 15 ppm or more. If the test measures CYA at 100 ppm, a dilution should be done for accuracy. A simple two-part dilution is 1 part distilled water added to 1 part pool water. Multiply the test result by two. Remember, CYA is very effective at protecting chlorine from the UV rays of the sun, but CYA also affects several other aspects of water chemistry.
Terry Arko has more than 40 years’ experience in pool service, commercial, retail and technical sales. He is a CPO Instructor, member of the Recreational Water Quality Committee of PHTA, board member of California Pool and Spa Association CPSA, and the head instructor of the Pool Chemistry Certified Residential course of Pool Chemistry Training Institute PCTI.