Normally around here, we talk about how to add chlorine to your pool or spa, but today we discuss how to remove chlorine from pool and spa water (or ponds and fountains).
There are many ways to remove chlorine (and chloramines or combined chlorine) from water. Not all of these methods are suitable for large bodies of water or water with fish. For instance boiling the pool water, or employing reverse osmosis filtration, may be a bit drastic.
Measuring High Chlorine Levels
When testing very high levels of chlorine, 10 ppm is the maximum for test strips, and at higher levels than that DPD test samples will bleach out, or turn clear. If this happens, dilute your test sample with half distilled water, and multiply by two.
For example, shake out half of the water test vial and refill with distilled water, then multiply your test result x 2 to obtain readings above 10 ppm. The same can be done with test strips by mixing a cup of pool water with a cup of distilled water, or any water that has no chlorine or a known, lower chlorine reading.
Removing Chlorine from Water
Chlorine levels in water will naturally reduce with exposure to sun and time. Heating, aeration and agitation can accelerate chlorine loss. But if you want to reduce chlorine levels fast, there are some chemicals to do it.
For swimming pools and spas, the usual method is to use Sodium Thiosulfate or Chlorine Neutralizer, to reduce or remove high levels of chlorine. Hydrogen Peroxide solutions used as an oxidizer for biguanide pools, can also be used to remove chlorine from pool water - I know it sounds strange. A third chemical, also strange is Ascorbic Acid or Vitamin C, like Stain Free that can be used in pools, spas, and fountains to remove chlorine, but that can be pricey for a large body of water.
Sodium Thiosulfate: The most well known product is fast acting, economical and won't affect pool chemistry or have any odd side effects. Completely removes both free chlorine and combined chlorine (chloramines). Sodium Thiosulfate is a member of a family of reducers, and is the most commonly used reducing agent for chlorine.
Dosage: You add about a cup (8 oz) of the dry white crystals per 5,000 gallons of pool water, or roughly 1 oz per 100 gallons - to lower chlorine by 10 ppm. Check your pool water pH and adjust to within label instructions, and add directly to the pool or spa.
In pools and spas, you want to be careful not to overshoot the mark, or overdose the pool with Sodium Thio, or you may have difficulty adding new chlorine, temporarily at least. Sodium Thiosulfate will dissipate from most pools within a few days. Follow the label instructions carefully when using a chlorine remover, for recommended water balance and dosages.
A good resource is this sodium thiosulfate calculator on Koiphen.com - enter your pool size in gallons (or liters) and the current chlorine level in ppm, and it tells you how many ounces or grams of Sodium Thiosulfate to add to reduce chlorine to zero.
Hydrogen Peroxide: The same chemical that brought Billy Idol and Eminem to fame? Same stuff, except the pool oxidizer strength is over 10x stronger than the foamy antibiotic in the brown bottle, and is formulated for use in pools. Hydrogen peroxide (H2O2) is used as the shock oxidizer for biguanide pool care systems (not to be confused with the sanitizer product, which is not H2O2).
In fact it is a quite powerful oxidizer that kills everything, including chlorine with the power of hydrogen and oxygen. These chemicals, sold under names like Baquacil, Revacil, Splashes or AquaSilk are an expensive way to remove chlorine from pools, and are not actually an intended purpose of the product, so no dosage or application instructions are available.
Ascorbic Acid: Another reducer that can be used to remove chlorine from pools, it is sold in many forms including Vitamin C tablets. We sell a formula that is used primarily for stain removal, called Stain Free.
Natural Chemistry makes Stain Free, an Ascorbic Acid based stain remover. According to the company, they do not market the product as a chlorine removal chemical, but it does remove chlorine in pools within normal pH ranges. No testing or dosage information is available, but they did tell this reporter that Stain Free may be a more expensive option than using Sodium Thiosulfate (Chlorine Neutralizer).
There are many other chemicals or conditioners that are used for chlorine removal in water for specialized uses, like aquarium, food and beverage, medical and industrial water, but for pools and spas (and fountains and ponds) - the most used chlorine remover is still good old Sodium Thiosulfate (Chlorine Neutralizer).
SPP Pool Expert