Total Dissolved Solids in Swimming Pools

Having a swimming pool is certainly a lot of fun, but taking care of it can be time-consuming and laborious. Today, we’re going to cover TDS, or total dissolved solids, a term you may have heard floating around. We’ll cover what TDS is, how to measure it, ideal TDS levels, how to reduce those levels if you need to, and more. Let’s get into it.

What are Total Dissolved Solids (TDS), and Why Do They Matter?

Total dissolved solids, or TDS for short, is a measurement of all of the solids that have dissolved into your swimming pool water. This includes both good and harmful substances that have dissolved into your water. While not an exhaustive list, the most common TDS are:

  • Magnesium
  • Pesticides
  • Potassium
  • Calcium
  • Aluminum
  • Zinc
  • Lead
  • Copper
  • Arsenic
  • Iron
  • Chlorine
  • Sodium
  • Fluoride
  • Bicarbonate
  • Sulfates
  • Chloride
  • Herbicides

Some of these are chemicals you intentionally add to keep your pool clean and safe for swimming, like chlorine. Others may have entered the water through rain, runoff, or as a result of leaves and other debris falling into your pool. Learning how to monitor and manage your TDS level is key to keeping your swimming pool in tip-top condition all year round.

How to Measure TDS

Measuring the TDS level of your swimming pool is the only way to get a picture of what exactly is in the water and know whether it is safe for swimming. If you are wondering what is in your water, here is a quick guide on how you can effectively and accurately determine what solids have dissolved in your swimming pool.

The easiest and most accurate way to measure your TDS level is with a TDS meter. This will provide a reading of the milligrams of solids dissolved per liter of water (mg/L). A score of 150 mg/L is considered a low score. This means that for every 150 mg of dissolved solids, there are 999,850 liters of water.

According to the Environmental Protection Agency (EPA), drinking water should not contain more than 500 mg/L. But, we’re not talking about drinking water here. Water containing more than 2,000 mg/L (in a freshwater pool) is considered unsafe for swimming and indicates an issue with your filtration system.

While a TDS meter will provide you with an accurate measurement of the quantity of solids in your water, it will not break down the contaminants, and to break them down you need to know which contaminants are in your pool – some dissolved solids are good, whereas some are not so safe.

To find out what elements are in your water, you will need a home water test kit or a lab water analysis. This will give you a clear picture of what is in your swimming pool and if it is clean and safe to use.

If you do not feel comfortable measuring your TDS level yourself, you can hire a pool cleaning expert to take these measurements for you. Whether you choose to do it yourself or consult a professional, knowing your TDS level is essential to confirm that your swimming pool is safe and your filtration system works effectively.

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Why is TDS Always Rising?

One thing you will quickly notice with your TDS level is the fact that it is continually rising. In fact, commercial swimming pools that use liquid chlorine can have their TDS levels increase by thousands of mg/L every year. This happens for a multitude of reasons. When you add chlorine to clean the water, this will cause the TDS level to rise. The TDS level will also increase when people are swimming in the pool.

Environmental factors, water quality, and a faulty filtration system are also common causes of a rising TDS level. The TDS level will rise quicker in warm climates as a result of evaporation too. As water evaporates and leaves your swimming pool, the ratio of contaminants to water increases. This is why maintaining a pool in warm climates can be a little bit more expensive and difficult.

A high TDS level can be a serious issue depending on what compounds are present in your pool. Chlorine is obviously a sanitizer you want in your pool and is pretty easy to raise and lower depending on the reading you get. Common contaminants such as arsenic or lead are toxic in high quantities, but many contaminants can make it tougher to keep your pool water chemistry in balance.

In particular, a high level of total dissolved solids in your water can make it very difficult to maintain an appropriate chlorine level in your pool. The solids reduce the activity of free chlorine, leading to decreased sanitation and unwanted algae growth. Furthermore, a high TDS level can be corrosive to the metal in your pool, like railings or steps.

Ideal TDS Levels for Pools

Now that we have established what a TDS level is and why it is constantly rising, let’s cover the ideal TDS level for your pool. Whether you have a freshwater or saltwater pool in your backyard, knowing and maintaining the proper level of TDS is critical to keeping it safe for swimming and relaxing.

Ideal TDS Level for Freshwater Swimming Pools

As a general rule, a lower TDS level is better. A level of TDS under 500 mg/L is practically unattainable. The commonly agreed-upon safe level of TDS is 500-2,000 mg/L. A level that exceeds this can be harmful to swimmers.

A TDS level above 2,000 mg/L in a freshwater pool can also indicate an issue with your water supply or your filtration system. If you measure the TDS level of your freshwater pool and it exceeds this amount, check out the tips below for how to reduce TDS levels.

Ideal TDS Level for Saltwater Swimming Pools

In a saltwater pool, the TDS level should be much higher than in a freshwater pool. Considering that regular tap water has a TDS level of about 500 mg/L, the salt content of saltwater adds about 3,000-3,500 mg/L to the TDS level. In addition, you must account for other contaminants that also naturally occur in a saltwater swimming pool. All of these combined usually result in a TDS level in the range of 5,000-6,000 mg/L.

So, the safe TDS level for a saltwater pool is considerably higher than for a freshwater pool. However, if the TDS level of your saltwater pool exceeds 6,000 mg/L, you may have issues with your filtration system.

Signs of High TDS

If you’re seeing any of these common warning signs, it’s probably time to check your TDS levels.

  • Your pool water is getting cloudy or has algae starting to form in it
  • Your water is salty and leaves a crusty film in the pool deck
  • You’re having issues maintaining a steady chlorine level after shocking your pool and your cyanuric acid levels are under 50 ppm
  • You’re starting to see excessive calcium scale deposits and your calcium hardness is under 400 ppm

Sound familiar? Use the steps below to reduce your TDS levels if you find them too high after testing.

How to Reduce the TDS Level in Your Pool

If you need to reduce the TDS level in your pool, installing a meter is a great way to monitor the level consistently. While a TDS meter does not specify what contaminants are in your pool, it does show what the level is, meaning you will be able to see how your TDS reading is trending.

Here are a few steps you can take to lower the TDS level effectively:

  1. Make sure your pool filter is running long enough during the day, at least 8 to 9 hours.
  2. Check your filtration system to make sure everything is working properly and change out the filter. This should be a regular part of your pool maintenance routine as a good quality filter will remove solids from your water. However, it may be time to troubleshoot your filtration system if you have a high TDS level.
  3. Check your water circulation. Make sure your valves are working properly and your skimmer basket and pool pump aren’t clogged up.
  4. Test your pool water to check your water chemistry. Make sure pH, alkalinity, cyanuric acid (CYA), calcium hardness, chlorine levels, and phosphate levels are all within range. If they aren’t, head over to my chemistry guide for some tips on getting your balance back in order.
  5. If all else fails, it’s probably time to drain your pool and add fresh water.

Wrapping Up

Alright, there you have it. So, to recap:

  • Don’t be afraid of your TDS levels, a lot of them occur naturally and good dissolved solids help you sanitize your pool.
  • Test your pool water frequently to figure out which levels are getting out of balance.
  • Act quickly to squash the issue before it becomes a problem!

Any questions? Let me know.

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