SLAM (Shock Level And Maintain)
Also called: Shock Level And Maintain, SLAM process.
SLAM stands for Shock Level And Maintain, the name Trouble Free Pool gives to the method that clears algae: raise free chlorine to the shock level for the pool's cyanuric acid (CYA), about 40% of CYA, and hold it there by retesting and re-dosing until the pool passes three exit tests.
Why it matters
One dose of shock does not do this, because chlorine gets consumed fighting the algae and drops within hours. Use plain liquid chlorine, retest and re-dose back to SLAM level 3–4× a day, brush daily and run the pump 24/7. You are done only when all three are true: combined chlorine is 0.5 ppm or lower, overnight chlorine loss is 1.0 ppm or less, and the water is crystal clear. It takes a FAS-DPD drop kit, because strips cannot read chlorine that high. Turn off any salt system while you SLAM.
In numbers
SLAM level by CYA: CYA 30 → 12, 40 → 16, 50 → 20, 60 → 24, 70 → 28.