Do You Need Algaecide?
The myth You need to add algaecide regularly to keep algae away.
Algaecide isn't a routine chemical. If you keep free chlorine at the right level for your CYA, algae never gets a foothold and algaecide has nothing to do. The one worth keeping on hand is Polyquat 60 — and really only for winterizing a closed pool. Avoid copper-based algaecides (most pool-store bottles): copper stains your surfaces and turns blonde hair green, and the only way to get it back out is to drain the pool.
Algaecide sounds like insurance: a little every week, no algae ever. In practice it’s a bottle doing a job your chlorine already does — and the cheap ones can leave you with a stain problem worse than the algae.
Chlorine is the algaecide
Keep free chlorine at the target level for your CYA and algae never gets going. That’s the whole prevention program. Algaecide is a backup for a job that’s already covered — which is why Trouble Free Pool doesn’t recommend it as a regular addition. If algae shows up, it’s because free chlorine slipped below what your CYA needs, and the fix is chlorine (a SLAM), not a weekly cap of algaecide.
If you’re dosing algaecide every week and still getting algae, that’s the tell: your chlorine is too low for your CYA. The algaecide was never the missing piece.
Avoid copper — it’s a one-way door
Most pool-store algaecides are copper-based, and copper is a trap. It doesn’t break down — it builds up, stains your pool surfaces, and turns blonde hair green. The only reliable way to get copper back out of the water is to drain and refill. A $15 bottle can create a problem that costs a full drain to fix.
The one worth keeping (the honest edge)
If you keep any algaecide on hand, make it Polyquat 60 — the most effective quat-based algaecide and the gentlest in a chlorinated pool. Its real use is winterizing: a preventative while the closed pool sits for months. That’s a specific job, not a weekly habit.
Do this instead
Hold free chlorine to your CYA target (the FC/CYA chart), and if algae ever appears, SLAM it. Routine algaecide belongs on the same shelf as the rest of the pool-store upsells — the stuff that treats a symptom of chlorine being too low for your CYA. Less is more.
Frequently asked
Do I need to use algaecide in my pool?
Not as a regular addition. Algae is prevented by keeping free chlorine at the right level for your CYA — do that and algaecide has nothing left to do. Trouble Free Pool doesn't recommend routine algaecide; the only one it suggests keeping is Polyquat 60, and mainly as a preventative during winterization, not a weekly or monthly dose.
What algaecide is safe to use?
If you use one, Polyquat 60 is the pick — it's the most effective quat-based algaecide and causes the least trouble in a chlorinated pool. Its best use is during winterizing, when the pool sits unattended. Avoid copper-based and cheap 'quat' algaecides sold at pool stores; the quats can also cause foaming.
Why should I avoid copper algaecide?
Copper doesn't break down — it accumulates. In the water it can stain pool surfaces and turn blonde or light hair green, and the only reliable way to remove copper is to drain and refill the pool. A cheap copper algaecide can cause a staining problem that costs far more to fix than any algae it prevented.