Fixing Free Chlorine Level (FCL) Problems in Saltwater Swimming Pools

Last Updated: | By Barack James

How to Fix Free Chlorine Level Problems in Saltwater Pools

One advantage of a saltwater swimming pool over non-saltwater is that you don't need to measure free chlorine level (FCL) frequently and adjust it by adding harsh chlorine manually.

Saltwater Chlorine Generator (SWCG) produces chlorine and adds the right amount to your water to maintain recommend FCL. 

However, one potential issue of a saltwater pool is high or low free chlorine levels, especially for the new users of saltwater chlorine generators.

Since chlorine demand in saltwater or any other pool depends on several factors like water temperature, room temperature, seasons, and how busy your pool is, it's important to be aware of how to regulate the amount of chlorine your saltwater generator is producing and adding into your pool.

Always, to avoid FCL issues in your pool, make it a routine to measure free chlorine level in your water at least after a couple of days, and adjust the percentage settings in your SWCG to increase or reduce FC level depending on the reading you find.

Chlorine generators will only work with the settings you set in it. The frequency of testing your FC level should be determined by the factors considered earlier in the third paragraph.

For a practical example, if your pool is very busy the whole day every day with many swimmers, your pool will need more chlorine than a pool that is less busy and with few swimmers.

So, make it a routine to adjust the percentage settings in your chlorine generator low or high depending on chlorine demand in your pool or spa.

Here are among the best pool chemical test kits you can choose from to help you maintain your FC, TC, TA, CH, pH, Cyanuric acid, and Bromine for bromine maintained pools.

Can I Add Harsh Chlorine Manually in Saltwater Pool?

Saltwater chlorine generators are designed to produce small amounts of chlorine but consistently to maintain the ideal free chlorine level in your water.

You can regulate the amount of chlorine your SWCG produces by adjusting its percentage setting up or down to increase or decrease FC level in your water respectively.

However, if you have cloudy water, algae, or ammonia in your pool, your chlorine generator is not cable of producing sufficient chlorine to clear your water or kill algae and ammonia, especially when your SWCG has reached a very high percentage but free chlorine level is still low and water cloudy. 

In such a case, you will have to switch off your saltwater generator and add harsh chlorine manually to clear cloudy water or eliminate algae and ammonia, then put SWCG back on when FCL is stable and your water clear so that it maintains recommended FC level. 

Why is Free Chlorine Level High/Low in My Saltwater Pool?

Like you learned earlier, you need to measure and adjust the FC level in your water by adjusting the percentage settings in your saltwater chlorine generator.

The higher you set the percentage in your saltwater generator, the more chlorine it will produce, and the more FCL will be high in your water. 

You only need to raise FCL when it's low or reduce it when high and that should be done in the percentage settings of your chlorine generator after taking FC reading.

As such, never adjust your SWCG before measuring and knowing the level of FC in your water.

How to Determine the Correct SWCG Percentage Setting

To know the right SWCG percentage setting to produce the ideal level of chlorine for your pool, you have to be aware of few things and they are:-

1). Determine the right FC level for your pool. FCL in your water goes hand in hand with the level of Cyanuric acid in your water. 

2). Measure the actual FCL in your water and compare it with the appropriate FCL in your SWCG. Testing FC level should be done in the evening so that when it's low, you adjust your chlorine generator percentage setting appropriately. 

3). If the level of FC in your water is low, increase the percentage of your SWCG to produce more chlorine and reduce the percentage if the FCL is high. 

4). If the FC level is not balanced within an hour, wait for 48 hours and repeat steps 2 and 3 until your FCL is balanced with the Cyanuric acid level in your water. 

Causes of High FCL in Saltwater Pools 

FCL tends to get high in indoor pools, where the pool is not very busy and room temperature and water temperature are relatively lower, but the percentage setting in saltwater chlorine generator and/or pump run-time are set too high ending up in more chlorine production and high FCL in the end.

To reduce your FC level, reduce the percentage setting of your saltwater generator and/or pump run-time, which could be high.

To avoid a high FCL problem, measure your FCL frequently and adjust the percentage of your SWCG and pumps run-time as appropriate to regulate the amount of FC in your water.

Causes of Low FCL in Saltwater Pools  

On the other hand, if you have low chlorine in your saltwater pool, that means you are not adjusting your SWCG as required and the percentage is too low to produce enough chlorine to supplement used chlorine in your water.

Once again, you need to measure the FC level in your water frequently, especially after heavy pool usage and during hot weather, and adjust FCL by increasing the percentage setting of your SWCG to avoid cloudy water, algae, or ammonia.

 If you can't raise your FCL by adjusting the percentage of your chlorine generator alone, try increasing your pump's run-time too if that will work for you.

If unable to get your FC level higher and the percentage of SWCG and pump run-time are both very high, you could be having four issues to solve fast and they are:

1. Excess Cyanuric Acid: Cyanuric acid (chlorine stabilizer) is very powerful and consumes FC if high in your water causing high chlorine demand.

Measure and adjust your Cyanuric acid (Cya) level as required. The Ideal level of Cya for a saltwater pool is between 70 - 80ppm and should not go above that otherwise you will have a low FCL problem. View this chlorine/Cyanuric acid chart and know the correct Cya levels in a give FCL. 

Measure your Cya level and reduce it if high by draining and refilling part of your pool water, which apart from reverse osmosis, is the only practical way to reduce Cyanuric acid level in your pool.  

2. Early Stages of Algae: Early sign of algae is low FC levels in a swimming pool. To be sure you are dealing with algae, perform an Overnight Chlorine Loss Test (OCLT).

OCLT is simply adding a specific amount of chlorine in a pool in the evening and taking the FC reading in the morning to establish the amount of FC used up during the night.

If the FCL drops by more than 1ppm in the morning, you are dealing with young algae and you need to shock your pool manually but after shutting your SWCG because it cannot produce enough chlorine to clear your water.

3. Chloramine or Ammonia: High chloramine level causes cloudy water with low FCL. If you have ammonia in your pool, chloramine levels will be very high in your water and will require a lot of chlorine to get rid of.

Signs of ammonia in a swimming pool are extremely cloudy water, high combine chlorine levels, low Cyanuric acid levels, low FC level, and high chlorine demand in your water.

Just like eliminating chloramine and algae, you need to shut down your SWCG and shock your saltwater pool manually using harsh chlorine to get rid of ammonia in your swimming pool.

4. Calcium Buildups in Your Salt Cells: Chlorine is produced in the salt cell of a Chlorine Generator. However, since Calcium is used in the production of chlorine, Calcium scales always form and accumulate in the salt cell plates hindering sufficient production of chlorine that is introduced in the pool, leading to low free chlorine levels in your pool.

To avoid Calcium buildups in your chlorine generator's salt cells, you need to regularly inspect and clean your salt cell plates when you see white calcium flakes or scales in your pool to avoid low chlorine production.

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