Many of us have seen this happen: The pool operator shows up in the morning to start their day and they find out the pool’s free chlorine is over 10 or 20 ppm and they have to open in an hour! They hastily dump a large quantity of a chlorine neutralizer into the pool, without measuring, hoping it will bring the chlorine level down in time.
I often use the cooking analogy when talking about adding chemicals to a pool. It’s easy to add something to the water, it’s not so easy to remove it. There is a plethora of products out there designed to remove chlorine from the pool. Before we look at each, a quick note on pool chemicals. I will be referring to the chemical itself, not the product. Many of these products will have call themselves a chlorine neutralizer and have names like “CHLOR DOWN” or something that tells you what it does but doesn’t inform you what the actual chemical is. Always read the labels! Do not trust that the product being sold to you is safe for pool water. On the label it will tell you what the active ingredient is. Read up on it. Now let’s take a closer look at some methods used to remove chlorine from water.
Common chemicals used to remove chlorine from pool water include sodium thiosulfate, sodium bisulfite, sodium metabisulfite, calcium thiosulfate. Sodium thiosulfate is, by far, the most popular.
What all of these chemicals have in common is:
- They contain sulfates. Sulfates can damage concrete and more. Read more about sulfates.
- They reduce oxygen in the water. This is not an issue unless the water is being discharged into local waterways. (Do you know where you water discharges? If you’re not sure, find out! It could end up in local waterways and harm fish and other wildlife.) Fish need that oxygen to breath in the water. Without it, they will die.
In addition, using these chemicals in pool water can have lasting effects. Often, once added, a chemical like sodium thiosulfate will stay active for days. This can cause chemical waste from constantly adding chlorine to combat the neutralizer and meet normal demand.
Another method, which is much less common, is to use ascorbic acid. Vitamin C. Vitamin C is actually good for fish, which cannot produce it naturally and must get it from their diet. You can watch a frenzy of fish activity anywhere water is discharged that has been treated with ascorbic acid. It also does not contain any sulfates. It is the safest chemical to use for dechlorination. The downside is that it costs more.
A study was performed analyzing all the various methods of dechlorination. In that study, it is stated: “Ascorbic acid is shown as the chemical of choice since it did not cause any water quality impacts in the field tests.” Read this study
Lastly, one final method of dechlorination is just time. Waiting for the chlorine to fade on its own. Some aquatic facilities move all discharge into a holding tank, where it sits until the chlorine has dissipated. If possible, I always recommend waiting for water to come down naturally.
Whatever method you use, care should be taken when dechlorinating water. Chemicals should always be carefully measured and only what is needed added. Remember: You can always add more, but you may not be able to take it back out.
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