Guide
Pool Shock vs SLAM — What’s the Difference?
Pool shock usually means a one-time FC boost; SLAM means holding high FC until algae is gone and overnight loss is low. Here’s how to choose.
Search “pool shock” and you’ll get bags of cal-hypo, marketing claims, and conflicting ppm advice. Search “SLAM” and you’ll get a multi-day protocol. They’re related — not synonyms.
Pool shock (common meaning)
A shock is a one-time (or occasional) raise of free chlorine — after a party, a storm, or a mild FC dip. You add product, circulate, and hope FC lands somewhere useful. Fine for maintenance bumps. Weak as a plan for pea-soup green.
SLAM (protocol meaning)
SLAM means hold an elevated FC target (based on CYA) until the pool is clear and overnight FC loss is small. It’s brushing, filtering, and re-dosing all day, not one bag at dusk. Details: SLAM method explained.
Quick chooser
| Situation | Likely path |
|---|---|
| Water clear, FC a bit low | Normal chlorine dose / light shock |
| Cloudy, FC OK, filter dirty | Clean filter / circulate; retest |
| Green, walls slimy, FC crashes overnight | SLAM (or professional help) |
| “I shocked yesterday, green today” | You needed sustained FC, not one shot |
Product note
“Shock” on a label often means cal-hypo or dichlor at a high dose. Cal-hypo adds calcium; dichlor adds CYA. Liquid chlorine raises FC without those side effects — popular during SLAM for that reason. See chlorine calculator.
Track which one you meant
In your log, note whether you did a maintenance bump or a clearing protocol. Pooldex’s SLAM assistant is for the second case; everyday verdicts cover the first.