Can The Salt Level In My Pool Plummet Overnight?

Can The Salt Level In My Pool Plummet Overnight?

I read a comment online from a salt water pool owner who suggested that their salt level dropped from 3200 ppm to 400 ppm overnight. They didn’t say how they’d measured the two levels but I’ll assume it was a live instant reading from their chlorinator.

My Hayward AquaRite chlorinator system offers a live instant salt reading and while I’ve seen it toggle up and down by 100 ppm, I’ve never seen it drop that much. Which leads me to believe that in fact whatever measuring method this guy was using, was flawed or otherwise wrong.

While salt will be lost in your salt water pool when draining water, from splashing and leaks, salt does not evaporate and the salt level should not drop drastically for no reason. Your chlorinator or other measuring device might be malfunctioning if a sudden salt level drop is noted.

Below we’ll discuss how to test for salt in several ways, the main reasons for salt level decreasing in your pool and also some myths and rumors that need to be cleared up regarding salt usage in your pool.

Why is the salt level in my pool dropping?

Salt does not evaporate so we can clear that up to start with. While people think that salt needs to be replaced because water evaporates, the salt in the water does not just disappear due to water evaporation.

Water evaporates but salt does not.

There are however several reasons why salt is lost in the pool.

They include:

  • Splashing and other pool-related water loss.
  • Back washing your filter if you have to do so.
  • Draining water from your pool when the level gets too high i.e. after a heavy rainfall.
  • Due to a leak in the pool that causes water loss over time.
  • Draining water from your pool at closing time in the autumn.

Draining large amounts of water from your pool by necessity like filter back washing, drainage due to overfilling or pool closing in the fall are key reasons that large amounts of salt will be lost.

Typically, you will add salt at pool opening in the spring and perhaps midway through the pool season in the summer.

How quickly can the salt level in a salt water pool drop?

You will typically add salt to your pool in the spring when you open it and perhaps once or twice during the season. You may need 1-2 bags in spring and 1-2 more bags during the season. If you have a D.E. or sand filter that requires back washing, you might need to add salt more frequently as some does get lost during this process.

But the salt level in your pool does not drop that much during the season unless significant water is otherwise being lost i.e. through leaks, splashing or the aforementioned draining or back washing the filter.

The salt level in your pool should not change drastically overnight or even over a few weeks unless water is lost through drainage. If your chlorinator salt reading is showing a huge sudden drop in salt, check the salt level using a secondary source such as a salt test strip because chances are there is something wrong with the chlorinator reading.

How to test the salt level in your pool

The salt level in your pool should be in the range of 2700 ppm and 3400 ppm where 3200 ppm (parts per million) is a nice number to aim for. Follow your chlorinator’s instructions but that is the typical range.

There are several ways you can accurately test the salt level in your pool:

  • Using the instant salt reading feature of your salt water chlorinator if it has one.
  • Using salt water-specific test strips.
  • Using an electronic salt water tester like the one shown above in the main graphic.

Advice: Use two of the methods above so that you have a back up should one fail. So if your chlorinator has a live salt reading feature, grab a box of salt test strips as a back up or buy an electronic salt tester.

You can use the test strips or e-reader weekly as a back up to your chlorinator’s reading to ensure the salt level being reported is correct.


While salt is lost in a salt water pool due to lowering the water level (drainage), back washing, leaks, splashing and other events, the salt level should not drastically drop overnight or over a few weeks for no reason.

You will typically need to add salt at the beginning of the pool season and again during the season, more often if you back wash your filter.

Salt does not evaporate even when water does. Salt loss is due to other factors mentioned above but still not should not to a large degree over a short period of time.

Remember that it’s always easier to add salt to your pool than remove it!

Carl Mueller

I bought a home with a salt water pool in 2006 and soon realized the benefits over traditional chlorinated pools. On this website I'll discuss all the tips and tricks I've learned over the years. I'll also help you troubleshoot various problems with pools in general and ones specific to salt water pools that I've experienced personally!

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