Why do salt water pools need to have salt added to them on a regular basis, typically twice per pool season? There must be a reason(s) why pools lose salt and need it replaced. I decided to take a closer look and here’s a summary of what I found.
Salt water pools lose salt from the maintenance of some filtration systems as well as swimming activities such as splashing and dripping bathing suits. Water leaks are also common losses of salt and draining a pool whose water level is too high contributes as well.
Several popular myths also exist regarding salt loss from your salt water pool and people often assume that it’s due to reasons that aren’t even real so we’ll talk about them in this article too.
Here are 5 reasons for salt loss in your pool and what you can do to prevent each.
1. Backwashing your filter
If you own a cartridge filter you can skip this first reason. But if you have a sand filter that requires backwashing keep reading. And if you are planning a water filter purchase and are deciding between various pool filtration systems, you should also keep reading because this is a major downside to sand and other pool filters:
Backwashing.
Backwashing a filter means that you rinse the filter out to remove contaminants that have accumulated by using water from your pool that is run through a hose and exiting typically on your lawn or driveway.
The purpose of a pool filter is to remove small contaminants and debris from the pool water as it passes through the pump and chlorinator before returning it to the pool. Over time, the filtration system gets full of debris, the internal pressure of the filter raises, and its ability to filter debris decreases. It’s like a garbage bin that gets full and needs to be emptied.
Every time you use the Backwash features, it runs water through the sand inside the filter to clean it out. Each backwash cycle typically means running water out of the pool for about 2 minutes or until the water runs clear on the sight glass on the filtration unit. This can mean 150 – 300 gallons of water lost during this time, including any salt that is contained in that water.
It’s usually recommended to backwash your filter once the pressure on the filter increases by around 8 psi – 10 psi over the starting level. This may occur every 14 days or so during the summer season. So it’s important that you write down or mark the “normal” starting pressure on your sand filter right after it has been backwashed so that when it goes up by 8 psi – 10 psi in the next few weeks, you can backwash again.
A sand filter also uses a Rinse feature that is used once backwashing is completed. It usually lasts for 30 seconds – 1 minute in length and involves flushing more water out of your pool through the filter to flush out any last debris and contaminants from the filtration unit and piping which again leads to more water and salt loss.
Cartridge filters do not require backwashing but instead require occasional rinsing of the cartridges which are the filter mediums themselves. You remove them from the filtration unit and wash them off so the loss of salt in this instance is minimal.
Solution
If you have a pool filter system that requires backwashing, carefully follow manufacturer instructions and only backwash as often as is required. Over backwashing is common among pool owners and not only does it lead to more water (and thus salt) loss, it can throw pool chemistry out of balance which takes time and effort to get back in line. Plus some jurisdictions frown on excessive pool water dumping into sewers which can cause you grief if a neighbor reports you. When it’s time to replace your pool filtration system, you might consider a new one that doesn’t require backwashing such as a cartridge-based model.
2. Spillage from splashing
Swimmers and particularly kids enjoy pools and splashing is one of the activities that often occurs. Jumping, diving and doing cannonballs also adds to water loss. If you have a water slide it’s likely that can add to splashing and further water loss which also reduces salt.
If you have a vinyl pool and the liner starts to come away from the side of the pools which is common over time, splashed water can end up spilling behind the liner and running down to the bottom of the pool foundation. Over time the water evaporates or is otherwise lost to the pool which again contributes to both water and salt loss.
If you have a waterfall or water feature that throws water high in the air, a windy day can help to contribute to water loss too. It all adds up.
Any time you have water loss like this, you will have salt loss too. It’s just a reality of pool ownership.
Solution
Probably not much you can do here. Pools are meant to be enjoyed and how can you prevent kids from splashing around and having fun? Compared to water loss from a backwash, it’s relatively minor too.
3. Water loss from bathing suits
People – particularly kids running in and out of the pool frequently – often track a great deal of water out of the pool when they jump in and out repeatedly. Adults take even more water out because they tend to be bigger and wear bigger bathing suits that hold more water.
This is again a reality of having a pool but it further helps to explain why salt is lost from a salt water pool.
Solution
Probably not much you can do here either. It’s just a reality of pool ownership that occurs and leads to both some water and salt loss. Just an FYI in case you’re still wondering why you lose salt.
4. Water leaks in your pool
This is a big one and a reason that can be limited if not outright prevented. If you have a vinyl pool, the liner can tear or rip and it can lead to water loss and leaks.
The concrete base of your pool can crack and leak as can underground or above ground piping.
A heater can leak and cause water loss as can your pump. This can occur from either the pump itself, around the seals of piping or even the skimmer basket if the brackets get loose and allows air and water to escape.
Your filtration system can also leak water if a valve gets loose or something isn’t tightened correctly.
Again, over time it can all add up to water and salt loss.
Solution
During pool season, water will evaporate naturally so it’s common to see noticeable water loss within several days of hot sunny weather. It’s not uncommon to see a 0.25″ to 0.5″ water loss in a pool on a daily basis which means a loss of 1.75″ – 3.5″ of water per week simply due to evaporation.
While evaporation won’t reduce salt content it can hide the fact that you are also leaking water. It’s important to familiarize yourself with “normal” water loss to notice when abnormal water loss occurs to spot a leak quickly. Inspect your pool daily and ensure brackets on your filter and skimmer baskets are tight and that there are no puddles or drips that shouldn’t exist.
5. Draining your pool level
After a heavy rain storm it isn’t out the question to see a water level increase up to several inches to the point where the water level is too high. A normal water level can typically be determined by eyeballing the skimmer on the side of your pool. Water should be able to flow into the skimmer about 1/2 to 3/4 of the way up the skimmer.
All you can do when the water level is too high is either wait for the water to naturally drop through evaporation and other things we’ve spoken about above. If the water is too high and needs immediate action, you have to drain water out. Draining water out of course will also remove salt.
If the water level gets higher than the top of the skimmer, not only will the skimmer not properly skim the surface of the pool and draw debris in which is its purpose, the higher water level tends to lead to more water and thus salt loss through splashing, diving, jumping, etc.
Solution
Before draining water out, only do so when it’s required. I’ve found that after a summer storm raises water level too high, the normal water loss that occurs in summer typically takes care of things and water level will naturally fall without draining. But if your pool is close to overflowing or is above the top of the skimmer, you’re probably going to need to drain some off. And salt will be lost.
A few salt water pool myths busted
While we have discussed the five main reasons that salt is lost in a salt water pool, there are a few reasons you may have heard that aren’t correct.
Salt doesn’t evaporate
Some people think evaporated water leads to salt loss but it does not. When water evaporates the salt level doesn’t change. Water evaporates but salt doesn’t.
In fact other than losing salt in the 5 ways mentioned above, if you do need to ever lower salt level in your pool, it’s generally done by draining water out and replacing the lost water with fresh unsalted water. It won’t happen by evaporation.
Salt doesn’t wear out
Salt also doesn’t wear out or die. While the salt cell that processes your salt and converts it to chlorine will die and end up needing to be replaced, you replace salt in your pool because of salt loss for the reasons described above and not because the salt dies out.
Summary
Salt replacement in a salt water pool occurs on an as-needed basis. Having a salt water chlorinator system that measures a live salt reading is handy to keep you informed as to current salt levels so you can add salt if needed.
It’s important to note that it’s easier to add salt to a pool than remove it so do be careful when adding salt and only do so when needed. The ideal salt level in a salt water pool is 2,700 ppm – 3,400 ppm with 3,200 ppm being a goal that is good to aim for.
