The SLAM process is the best way to eliminate algae, sanitize your pool, and achieve crystal clear water. You cannot complete this process overnight! Allow for several days to finish and do not take any shortcuts! A SLAM cannot be completed unless you are willing to do your own testing with a FAS-DPD chlorine test, included in our recommended test kits and also available separately. Without that specific test, you risk wasting your time and potentially having to start all over later.
When should I SLAM?
If you have ANY of the following:
- Visible algae in your pool
- CC level above 0.5 ppm
- Loss of 1.0 ppm of FC overnight (see overnight chlorine loss test)
Before you start:
- Obtain a FAS/DPD chlorine test, available in our recommended test kits
- Determine your current CYA level with a reliable test kit, and then look up the corresponding SLAM FC level using our FC/CYA tool.
- Purchase enough liquid chlorine or bleach to raise your FC from zero to SLAM level at least twice. Use our PoolMath calculator to determine this amount.
- Remove leaves and visible debris from the pool, as much as possible.
- Make sure your filter is working properly and you understand how to backwash and clean it out should it become necessary.
- Check and adjust the pH to between 7.2 and 7.5. The pH test isn’t reliable during a SLAM so adjust pH before you start. There’s no need to test pH again until your SLAM process is completed.
Perform the SLAM process:
- Test the FC level and add enough chlorine to bring FC up to SLAM level 3-4 times per day.
- At the beginning of your SLAM, the chlorine is used quickly to kill algae. As the algae is killed off, you can reduce your testing and chlorine additions to 2-3 times per day.
- We recommend testing after sunset and at sunrise to check if algae is consuming chlorine in the absence of sunlight (see OCLT).
- Brush and vacuum the entire pool once a day if you can. Brush inside skimmers, under main drain covers, on weir doors, inside ladders, and behind removable lights if applicable.
- Backwash or clean the filter when filter PSI increases by 25% over baseline.
- Vacuum up debris as needed.
- Run the pump 24/7 until you are done SLAMing.
Finish the SLAM
Once all three of these criteria are met, you have completed the SLAM process and can allow the FC to drop to normal levels.
- CC is 0.5 or lower
- AND your overnight chlorine loss test shows 1.0 ppm of loss or less
- AND pool water is crystal clear with no visible sign of algae (dead or alive) on floor and walls
Additional Notes:
In the first few days of a SLAM, testing and adding chlorine more frequently can be beneficial to closely maintain SLAM FC level. We recommend 3 times daily at a minimum: morning, noon, and night. If your schedule permits, you may test and add chlorine more often.
SLAMing an outdoor pool is most effective when CYA is around 30 to 40. Below 30 you lose too much chlorine to sunlight. As CYA goes up, SLAMing requires more and more chlorine, which starts to get impractical around 80 or 90. With CYA above 90 we recommend replacing water to decrease CYA before you start the SLAM process.
Depending on what kind of filter you have, it can take the filter a week or more to completely clear the water, even after all of the algae is dead. DE filters are usually much faster than that, but also require more frequent attention. Sand filters are the slowest, and cartridge filters are somewhere in-between. Nevertheless, each filter will get your pool crystal clear.
While SLAMing, the appearance of the water should improve each day, though perhaps only by a little. If you fail to see any improvement you might have a problem with your filter, you might have a higher CYA level than you think, you might have poor water circulation, or you might have some other more complex problem. Start a thread on our forums and we can offer you personalized advice.
The goal of SLAMing is to add enough chlorine to oxidize all of the algae, combined chloramines, bacteria, viruses, ammonia, and other organic contaminants. Oxidation breaks down the organic molecules into smaller parts which are harmless. When SLAMing, you need to keep adding chlorine until the breakdown process is complete.
Higher FC levels will oxidize contaminants more quickly, but levels that are too high can cause damage to the pool or the pool equipment. Our SLAM FC levels are designed to break down contaminants quickly while posing no risk to the pool or anyone swimming in it. It is impossible to know in advance just how much chlorine will be required to SLAM the pool. Instead, chlorine is added to maintain SLAM level until testing shows that the process is complete.
Though your free chlorine levels may seem high, you can safely swim in your pool so long as you can see the bottom. This means that you can safely enter your pool to scrub hard to reach places even at SLAM FC. If you exceed SLAM FC, we recommend allowing the FC to drop to SLAM level before swimming.
If you have a salt water chlorine generator, chlorine tablet dispenser, injection pump, or Liquidator, turn it off for the duration of the SLAM process. SLAM by adding liquid chlorine only for best results.
If you have a sand filter, you can speed up the process by adding a little pool-grade DE to your filter. See Add DE to a sand filter for more information.
If you have questions that aren’t covered here, start a thread on our forums and our experts and guides will assist you quickly.
