Using Bleach to Maintain a Crystal-Clear Swimming Pool
One of the classic problems with owning a pool is that it can be a costly headache to maintain water clarity and balance. The brochures make it look easy to obtain perfectly balanced, crystal-clear water. However, trying to achieve this can be expensive and frustrating, often resulting in multiple trips to the local pool store, where you’ll hear all sorts of costly misinformation.
Chlorine is by far the most commonly used swimming pool sanitization agent. The goal of adding chlorine to a pool is simple: kill microorganisms such as bacteria and algae. A pool with excessive bacteria and algae is cloudy and unsafe to swim in. The chemistry behind the ability of chlorine to kill is straightforward. Chlorine is a negatively charged ion that can rip through the outer membranes of the microbes, destroying them and rendering them harmless and unable to grow. The most readily available form of chlorine is liquid bleach, which is chemically known as hypochlorous acid (the bottle of bleach will list sodium hypochlorite, the salt of this weak acid), a form of chlorine bound to a negatively charged oxygen atom. Once the bleach is added to water, the hypochlorous acid molecule turns into a negatively charged hypochlorite ion and goes to work killing microbes and sanitizing your pool.
Most pool stores do not suggest that you use simple chlorine as described above. They sell long-lasting “hockey puck” tablets of chlorine that are combined with all sorts of other chemicals. These chemicals allow the chlorine to stay around for a long time, and may also include some algaecides. You might think it is a good thing to have additional chemicals to allow the chlorine to stay around longer, especially considering how quickly sunlight degrades chlorine. The problem, however, is that when chlorine is combined with these chemicals (a.k.a. “stabilized”), it is not nearly as effective at killing algae or bacteria.
Pool store chlorine tablets commonly include a chemical called “dichlor” or “trichlor.” These tablets include dichloroisocyanuric or trichloroisocyanuric acid, which are fancy ways of saying bound, or stabilized, chlorine. The problem is that when you add these tablets or “pucks” to your pool over time, the stabilizing chemical doesn’t break down very well and you can’t control the amount of it in your water. When this happens, the pool has an excess amount of stabilizer (cyanuric acid) and any new chlorine you add will be immediately stabilized and unable to kill any algae or bacteria in your pool. The algae and bacteria start growing, and in a few weeks, you’ll have a cloudy pool. Some people in the pool industry refer to this as “chlorine lock” – when your chlorine is mostly bound to stabilizer and is not an effective sanitizer. The pool store will then sell you additional chemicals (expensive clarifiers, algaecides, more stabilized chlorine, etc.) to make the pool clear again when the real problem is that you have all of your chlorine bound to a stabilizer and it can’t do its sanitizing job. The pool store gets rich and you are frustrated, with no real solution to your problem.
The solution to maintaining a clear pool is to use readily available liquid bleach as your chlorine source. Chlorine bleach, as discussed above, is not bound to a stabilizer, so when you add chlorine bleach to the pool, it will go right to work killing microbes and sanitizing. Daily adjustment of bleach to your pool water will result in a relatively constant level of active sanitizing chlorine that will be cheaper and easier to maintain over time.
When you add your chlorine this way, however, you will need to add a small amount of stabilizer to your pool so the sunlight doesn’t destroy all of your chlorine the instant you add it in. In this case, since you are controlling the amount of stabilizer, you are assured that you aren’t over-stabilizing the pool and your chlorine will be actively sanitizing, if chlorine levels are maintained. You can buy cyanuric acid (stabilizer) from the pool store or a big-box store and add it once at the beginning of summer and most likely not again for a few months, as opposed to adding it daily or weekly with chlorine tablets. Once your pool has a steady and correct amount of stabilizer in it, it will protect and stabilize a certain amount of your chlorine while allowing a more appropriate amount of non-stabilized chlorine to do its sanitizing job.
How Much Chlorine To Add?
Some fantastic online pool math calculators like this one exist to help with the question of how much chlorine to add. For example, for my 25,000-gallon pool, I maintain a cyanuric acid level of 30 parts per million (ppm). To raise the free chlorine by 1 ppm, I add about 40 ounces of an 8.3 percent bleach solution, which is about a third of a jug of bleach. You can scale up and down accordingly; if you need to raise the free chlorine by 2 ppm you would add about 80 ounces. Using the table in Illustration 3, if you keep your free chlorine above the minimum recommended value, you should have a clear, sanitized pool with no issues.
Depending on how many people use your pool (“bather load”) and its location, your pool will have a chlorine consumption rate that will become apparent to you once you start routinely testing.
You should add the chlorine just after the sun sets. The following day, it will slowly drift down (naturally breaking down by sanitizing and being exposed to sun). The next day you will test and adjust the level again. A pool with low chlorine demand (not many people, and mostly shade) might consume about 0-1 ppm of free chlorine per day. A high-use, full-sun pool might consume about 3-4 ppm per day or more.
Home testing is critical to maintaining a clear and balanced pool. You should test your chlorine levels daily to make sure your chlorine levels are adequate. Daily testing might sound cumbersome, but it is rather simple once you know how to use a standard DPD test kit, which accurately determines the amount of free chlorine. These test kits are available on the Internet or in pool stores. Be sure to avoid the more common OT test kit, which is not as accurate. In general, using a DPD test kit involves measuring a small amount of your pool water into a test tube. You then add a small amount of the DPD chemical, which immediately turns chlorinated water pink. You then add another chemical until the pink color disappears, counting each drop you add. Most kits have you take that number and divide it in two for your free chlorine level. You can then increase your pool’s chlorine amount by adding bleach per the table in Illustration 2.
Cyanuric acid (chlorine stabilizer) test kits are also available to test your pool for stabilizer levels. These kits involve adding pool water to a chemical solution and using an easy comparison reference based on cloudiness to determine how much cyanuric acid is in your pool. If your levels are low, cyanuric acid can be added by purchasing it in liquid or powdered form. The instructions on the cyanuric acid container will say how much to add to increase levels.
Some readily available high-quality test kits include the Taylor K-2006 and the TF-100 test kit, both easily available online.
From experience, my pool, which is a 25,000-gallon in-ground pool located near the woods (lots of leaves and tree debris) with a rather high bather load (including lots of kids), will use about 1-3 ppm of chlorine per day. A typical bottle of Clorox bleach is 121 ounces of 8.3 percent sodium hypochlorite. Adding about 1-3 ppm for my 25,000-gallon pool costs about $1.20-$3.60 per day. In a month, the amount of money you spend on chlorination via bleach starts at about $30. If you have been to a pool store to solve a cloudy pool problem, you are well aware that you can leave having spent hundreds of dollars in one day and your problem will most likely return the following week! Walmart routinely sells liquid chlorine at 10 percent concentration for about $2.50, for a significant cost savings for pool sanitization.
If your pool does become cloudy using this method, the way to fix it is to raise your chlorine levels to the shock level described above and hold the level there overnight by adding more bleach as needed. For most situations, this will be adequate to resolve the problem, and you can resume normal chlorination the next day.
In summary, to start with this method, purchase a high-quality test kit with a DPD chlorine test and a cyanuric acid stabilizer test. Test your water per the test kit instructions. Then, using the math discussed here, add the appropriate amount of cyanuric acid to start off with 30 ppm. If you are already there, don’t add any; if you are too high you will need to drain some of your water and refill.
After your cyanuric acid level is set, add the bleach. Then proceed with daily testing until you understand how much chlorine your pool uses. At this point, chlorine maintenance can be as simple as adding a little bleach to your pool every day to keep it within the target levels. This method is a cost-effective and highly successful method for keeping your pool crystal clear all summer long.