To SLAM a swimming pool or spa, is the process of adding chlorine in your pool or spa to reach and maintain high free chlorine (FC) shock levels, with the purpose of getting rid of either algae or ammonia in a swimming pool or spa... so you know SLAM is not a pool chemical.
There is no shortcuts to getting rid of algae or ammonia, SLAM process needs patience and you cannot achieve results in a single day.
You will need to add non-stabilized chlorine (Sodium Hypochlorite) in your pool at least twice a day for a couple of days or even longer in order to kill all algae in your pool.
Even worse, if you are fighting ammonia in your pool, you will have to measure FC level every 15-20 minutes and add more chlorine when it reduces to some level; ammonia has high resistance to chlorine and consumes more of it when you start the SLAM process, and the hard you it in the initial doses the faster ammonia will go.
If you have been maintaining recommended FCL in your pool or spa by adding chlorine frequently, you don't need the SLAM process, unless you have ammonia or algae in your pool.
Since the SLAM process involves testing FC levels and adding more chlorine in a swimming pool, you need to be aware of your Cyanuric acid (Cya) or chlorine stabilizer level so that you raise your FC level depending on the level of Cya in your water.
Remember, the higher the Cya level in your water, the more chlorine you will use for the same effect, and that is why we recommend non-stabilized chlorine for SLAM process.
The recommended Cya level in a pool for a successful SLAM is between 30ppm and 40ppm, higher than that you will have to spend more on chlorine to be able to clear algae or ammonia.
For instance, if your Cyanuric acid level is 30ppm which is the lowest for an outdoor non-saltwater pool, the ideal SLAM level or FCL is 12ppm and the lowest FC level can go before adding more chlorine is 6ppm: This means that you will add enough chlorine to raise your FCL to 12ppm and maintain it there by adding more chlorine if it reduces to 6ppm.
If your Cya level is 40ppm, your shock level will be 16ppm and the lowest level free chlorine can go before adding more chlorine is 7ppm.
It is even header to clear algae or ammonia in a saltwater pool, this is because saltwater pools always need higher Cya level between 70ppm to 80ppm, and this will require more chlorine to raise and maintain FCL at 28ppm for 70ppm Cya and at 31ppm for 80ppm Cya.
This means that if your Cya level is higher than 40ppm for a non-saltwater and 80ppm for a saltwater pool, it is advisable to lower your Cya by draining and refilling a portion of your pool or spa water before starting your SLAM.
To understand the shock level to maintain in your pool depending on your Cyanuric acid level, refer to Chlorine/Cya Chart by trouble free pool.
Since clearing ammonia in a swimming or spa is harder and needs more initial doses of chlorine, after adding the initial chlorine to achieve your shock level depending on the level of your Cya, you will be measuring your FCL every 15-20 minutes every day and raising it back to your SLAM level by adding more chlorine, this might take a lot of chlorine and a few days to clear all the ammonia in your pool.
Just like clearing ammonia, clearing mustard or yellow algae may also need this kind of frequent water testing and addition of more chlorine.
However, if you are fighting black or green algae, you can measure your FCL at least after 3-6 six hours and raise it back to your shock level by adding more chlorine, which unlike clearing ammonia and mustard algae, might need at most only two additions of chlorine a day everyday until you clear all the algae.