Swimming Pool Blog
What Can You Learn From a Pool Water Test?
by Alicia Harris, July 20, 2018
What Can You Learn From a Pool Water Test?
Swimming pool test kits and test strips are essential for maintaining balanced, sanitary water in your pool. But what can you learn from a pool water test, and what should you look for when purchasing a test kit? Which factors should you pay closest attention to in your water? And more importantly, what does ideal water chemistry look like? Not to worry...we’re here to help! Depending on which swimming pool test kit or strip you purchase, you can learn a lot of different things about your water’s chemistry. Here are some of the things you can test for in pool water:
When kept within the ideal range of 80-120 parts per million (ppm), total alkalinity (TA) helps stabilize pH levels. It acts as an acid buffer to prevent rapid pH changes in the water. If alkalinity gets too high or too low, this can also cause water clarity issues, eye irritation, surface stains, wall erosion, metal corrosion in pool equipment, and your chlorine may lose some of its sanitizing power. Total alkalinity is typically the first thing you should address when balancing pool water, especially if you’re going to be altering the pH. TA can be adjusted with an alkalinity increaser to bring the reading up or a product like sodium bisulfate to bring the numbers down.
Measuring the pH of a pool will tell you if the water is too acidic or too basic. Good test results should fall between 7.2-7.6 on the pH scale, with 7.4 being ideal. Readings on the high end, or base side, can cause scale deposits and cloudy water, while low readings within the acidic range may corrode pool surfaces and equipment. Good pH can have a large impact on the ability of chlorine to work properly, so monitor your levels frequently to stay balanced. Use pH increasers (bases) and pH decreasers (acids) to adjust your rating.
On the same subject of pH, acid demand and base demand tests involve titration of your pH sample. The results help determine how much acid or base to add in order to balance the pH in your pool. Use caution, however. If total alkalinity is too high, this test can give incorrect results and you’ll end up adding too much acid to the water.
Much like total alkalinity helps keep pH levels balanced, cyanuric acid (CYA) helps to stabilize chlorine levels by reducing chlorine loss caused by the sun’s harsh UV rays. CYA (also known as conditioner or stabilizer) levels should stay within the 30-50 ppm range. It’s important to check this number before attempting to read chlorine levels, as high CYA (100+ ppm) can cause “chlorine lock,” preventing the existing chlorine from being active or even appearing in the free chlorine test. The traditional solution for high CYA levels used to be dilution: drain a portion of the pool and refill. However, a new product called Bio-Active reduces CYA levels in your pool without the need for wasteful draining. Some products like stabilized chlorine already contain CYA, so use caution to keep this reading within range.
There are several different types of chlorine in your pool: free, combined and total chlorine. The important thing to remember is that free chlorine is what’s keeping your pool sanitary and algae-free. As the chlorine is doing its job, chemical reactions with ammonia and nitrogen create combined chlorine (also known as chloramines) in the water. Combined chlorine is the “bad chlorine” responsible for strong chlorine smells, burning eyes, itchy skin, rashes, metal corrosion and other issues. Total chlorine, as the name implies, is a measure of all free and combined chlorine in the pool. You can find the level of combined chlorine in your pool by subtracting your total chlorine reading from your free chlorine reading (TC - FC = CC). If your free chlorine level is 0.5+ ppm lower than your total chlorine level, it may be time to shock your pool. We recommend starting with a pH around 7.2, and super-chlorinate your pool to 10 ppm in the evening hours. Free chlorine readings should always be around 1-3 ppm.
Most swimming pool test kits or test strips use the chlorine test to help you determine bromine levels in the pool. Since bromine is heavier than chlorine, the reading will need to be multiplied by 2.25 or you’ll need to use the right comparison chart included with the kit. If you are using bromine as a sanitizer in your pool, keep the concentration at about 2-5 ppm.
Copper and iron could be lurking in your water, waiting to stain the surfaces of your pool. Metals can come directly from the water supply, or they could be a symptom of pool equipment corrosion caused by pH, alkalinity or water hardness issues. Test regularly to prevent problems down the road. Products like Natural Chemistry Metal Free or the CuLator Metal Remover Pouch can help prevent aesthetic damage to your pool.
This reading is sometimes overlooked, but it’s just as important as the others. If calcium levels in a swimming pool fall below 100 ppm, the water will actually try to balance itself by leaching calcium from concrete, grout and plaster surfaces. Over time, this will damage the integrity of the pool, resulting in costly repairs. On the other hand, if calcium levels are too high (500 ppm or greater), scaling can become a problem. Recommended calcium hardness falls in the 200-400 ppm range. You can boost calcium levels with a calcium hardness increaser and reduce levels by diluting with softer water. If you already have high calcium in your pool, you'll want to avoid using calcium hypochlorite (cal-hypo) sanitizer or shock since this product will add some calcium to the water.
Total hardness is simply a measurement of the total calcium and magnesium content in a pool. Generally speaking, calcium levels equal about 2/3 of the total hardness reading. However, this rule of thumb will be inaccurate if you use a mineral sanitizer in your pool, since the magnesium levels will be higher than normal. There’s no negative impact from having too much or too little magnesium in your pool, so, if given the option, testing for calcium hardness is a more effective route than monitoring total hardness.
If using a salt water chlorine generator to sanitize the pool, you’ll need to monitor salt content from time to time. Salt chlorinators typically require 1,500-4,500 ppm salinity in order to work properly, but this number can vary between manufacturers. Some models actually show the sodium chloride concentration on the unit display, but it’s still a good idea to test levels from time to time to make sure the calibration is correct. Add pool salt as needed to maintain proper concentration levels.
Total Dissolved Solids
The total amount of dissolved materials in your water (salts, metals, minerals, organic material, chemicals, etc.) will be shown in a total dissolved solids test. A number of problems stem from high TDS concentration, including scaling, staining, salty or cloudy water and the ability of chlorine to sanitize a pool. Ideal TDS should be less than 2000 ppm, and high TDS levels may require partially draining and refilling the pool. Salt water pools may have a higher TDS reading because of the additional salt content.
Of course, there are many other things you can test for in a swimming pool if you’re having ongoing issues with water clarity or algae. Measuring things like oxidation reduction potential (ORP) or the presence of phosphates, nitrates and growing organisms can be helpful if your current water treatment plan just isn’t doing the trick. You can also test for the presence of other sanitizers like biguanide if you’re using chlorine alternatives in your pool. If you're looking for test kits, test strips, reagent replacements or digital water testers, PoolCenter has just what you're looking for!
Click here for other handy tips on balancing pool water, or click here learn more about water testing.