Pool algae guides
Algae in a pool always has the same root cause: free chlorine dropped below the minimum for your CYA level. The fix is shock-level FC, daily brushing, and sustained treatment until the overnight chlorine loss test passes. What varies is the algae type — green, mustard, and black each need a different approach, and recurring algae almost always has a systemic cause you haven't fixed yet.
How to Kill Pool Algae: Step-by-Step Guide
The complete algae treatment guide: identify the type, shock to CYA × 40%, brush daily, run the pump 24/7, and hold until the OCLT passes.
Pool Turned Green Overnight? Emergency Triage
A pool that turns green overnight has a fresh algae bloom from FC dropping below the CYA minimum. Triage in 5 minutes, then shock and hold to clear in 3–7 days.
Mustard Algae vs. Green Algae
Yellow-brown slime that brushes off but keeps coming back? That's mustard algae — chlorine-resistant, and it returns until you wash all swimsuits and decontaminate gear.
Black Algae in a Pool
Black algae (cyanobacteria) forms a hard shell and roots into plaster. Regular shocking doesn't work — it requires wire brushing before every chlorine dose for 1–2 weeks.
Why Algae Keeps Coming Back
Recurring algae has a root cause: FC below the CYA minimum, high CYA, incomplete treatment, contaminated equipment, or circulation dead spots. Find the pattern by tracking readings.
Dead Algae but Pool Still Cloudy?
Killed the algae but water is still hazy? Run filtration continuously, use clarifier or floc, and pass the overnight chlorine loss test before stopping treatment.
Green Water but Chlorine Is High?
High chlorine with a green pool usually means CYA is above 80 ppm — the stabilizer has locked up most of the chlorine's active fraction. The fix is a partial drain.
Track the pattern that stops algae before it starts
PoolChem Tracker logs every reading over time — so you can see when FC dips below your CYA minimum and act before a bloom forms instead of after.
