Clear a green pool fast. Discover your exact Free Chlorine target based on your Cyanuric Acid (CYA) level.
If your pool is green, cloudy, or smells strongly of chemicals, standard chlorine levels won't fix it. You need to aggressively raise your chlorine to "Shock Level."
Why do some people dump 10 bags of shock into a pool, yet it stays green? The answer is the relationship between Free Chlorine (FC) and Cyanuric Acid (CYA).
CYA acts like sunscreen for your chlorine, protecting it from burning off in the sun. However, CYA also binds to the chlorine, making it work slower. The higher your CYA, the higher your chlorine must be to effectively kill algae. If your CYA is over 60 ppm, it requires massive, sometimes impossible, amounts of chlorine to sanitize the pool. This is often referred to as "Chlorine Lock."
To actively kill an algae bloom (the SLAM method), your Free Chlorine target must be roughly 40% of your CYA level. For example, if your CYA is 40, your SLAM target is 16 ppm.
If your CYA is above 70 ppm, do not try to shock the pool. You will waste hundreds of dollars on chlorine. You must drain and replace some of your pool water to lower the CYA first.
SLAM stands for Shock Level And Maintain. Instead of just dumping a bag of shock into the pool once and hoping for the best, SLAMing requires raising your Free Chlorine to a specific, high target, and maintaining that exact level by testing and adding chlorine 2-3 times a day until the water is completely clear.
It is highly recommended to use Liquid Chlorine (Sodium Hypochlorite). Powdered shocks contain either Calcium (Cal-Hypo) or Cyanuric Acid (Dichlor/Trichlor). Adding massive amounts of powder during a multi-day SLAM will dangerously spike your Calcium or CYA levels, leading to severe scaling or permanent cloudy water.
No. You should not swim while SLAMing a pool. The chlorine levels are elevated to aggressive sanitizing targets that can bleach swimwear and severely irritate skin and eyes. Wait until the algae is dead, the water is clear, and the chlorine has dropped back down to its normal range (usually under 5-8 ppm) before swimming.
Shocking the pool sometimes fails due to high CYA (Chlorine Lock). Keep your pool clear by rechecking chemistry often.