Persistent Green / Cloudy Water
Treating With Flocculant (“Floc”) — What It Is, How It Works, and the Trade-Offs
Flocculant (often called “floc”) binds tiny suspended particles and dead algae into heavy clumps that sink to the floor so you can vacuum to waste. It can deliver overnight clarity — but it’s not a silver bullet. Expect water loss, refilling, and sometimes more than one vacuum to remove all settled floc. On sand/cartridge systems with weak flow, persistent cloudiness is common even after floc.
What Is Floc? — a settling agent
Flocculants are polymers that grab fine debris and dead algae, forming heavy “flakes” that drop to the bottom. Unlike clarifiers (which help the filter catch particles), floc aims to settle and remove by vacuuming to waste.
Goal: Settle → Vacuum to wasteWhen To Use / Avoid — set expectations
Use for stubborn cloudiness after algae kill, heavy pollen/dust events, or post-construction debris. Avoid if you cannot vacuum to waste (many cartridge systems), or when you can’t afford a major water drop.
Must have: Waste line or bypassPrep The Pool — chemistry & circulation
Test/adjust pH to ~7.2–7.4, get free chlorine to target (post-shock), empty baskets, brush walls/floor, and clean/backwash filter. Remove robots and take covers off. Run pump to mix evenly.
pH 7.2–7.4 • Pump ONDose Accurately — follow the label
Measure pool gallons and dose per manufacturer. Over-dosing can create gummy residue; under-dosing leaves fines suspended. If product calls for pre-dilution, mix in a clean bucket first (chemical → water).
Precision mattersMix Briefly, Then Power Down — let it fall
Circulate on filter (or recirculate/bypass if available) for 30–60 minutes to distribute. Then shut the system OFF completely. Allow 12–24+ hours for full settling (longer in cold water).
12–24h undisturbedVacuum To Waste — slow and steady
Set multiport to WASTE. Vacuum slowly in straight lanes from deep end to shallow. Avoid stirring clouds. Expect the water level to drop; refill as needed. Do not send floc through the filter.
Expect water loss • RefillAftercare & Re-Balance — finish strong
When done, switch back to FILTER, top up water, bleed air, and test/adjust pH, alkalinity, and chlorine. Backwash/clean filter if pressure rises. Brush again to remove any film.
Test & brush post-vacCartridge & Sand Filters — limits & workarounds
Cartridge: Most housings lack a waste setting; consider a vac-to-waste bypass or skip floc and use clarifier + deep cartridge cleaning. Sand: Works better, but channeling or old media may cause re-clouding.
Bypass needed on many cartridgesCommon Reasons Floc “Fails” — diagnose, adjust
Wrong dose, disturbed settling (pump turned on), vacuumed too fast, no waste line, or ongoing algae (low FC). Old/channeled sand or clogged cartridges can also recirculate fines.
Check FC • Media conditionSet Expectations — trade-offs & multiple vacs
Warning: Floc does not always clear a pool in one pass. It’s common to need 2+ vacuum sessions as more fines settle overnight. The trade-off is water loss + cleaning time vs. a pool that stays persistently cloudy.
Clarity often needs 1–2 vacs
