Green Pool Recovery Program
Purpose
A green pool is not a visit, it is a program with gates, and the shop that treats it as a visit loses on it twice: when the water regreens four days after it cleared, and again when the customer decides the recovery never worked. This procedure guarantees a recovery is released on a measured overnight chlorine loss, not on the water looking blue, and that the shock level is set from the pool's measured cyanuric acid rather than from a jug label. Those two rules separate a recovery that holds from one that clears the water and leaves live algae in the plaster pores.
It also guarantees nobody enters water they cannot see the bottom of, which is the fatality this trade produces at green pools.
Scope
Covers a residential or small commercial in-ground pool gone green, cloudy-green, or black-green from algae: pre-work assessment, the drain-versus-treat decision, the shock program, the daily gates, and the release criteria that return the pool to a normal route visit.
It does not cover routine algae prevention on a healthy pool, which is the algae treatment procedure, and it does not cover a pool that must be emptied, which is the drain and acid wash standard including its hydrostatic gate. Cloudy water with a normal residual and no algae is a filtration or chemistry fault and the cloudy water diagnostic owns it. Commercial pools carrying a health-department closure duty follow that authority's re-opening rule in addition to everything here.
Roles and responsibilities
| Role | Owns | Hands off |
|---|---|---|
| Recovery technician | Every test, every dose, brushing, filter management, the daily log line | Hands the day's log line to the service manager same day, including days the gate failed |
| Service manager | Scope agreement, day count authorization, the release decision | Hands the customer a written no-swim notice with the barrier condition before day one begins |
| Customer | Barrier secured, no entry, pump running as instructed, no chemicals added | Confirms in writing that nothing was added between visits; an unlogged customer dose voids that day's gate |
Procedure
Secure the pool against entry before any test or dose. Opaque water hides the bottom, the main drain, and a body. Confirm the barrier gate self-closes and self-latches, confirm any pet or child access route is closed, and hand the customer a written no-swim notice naming the release condition. Accept when the gate latches from a released position without a push. Wrong looks like a propped gate or a missing latch: do not begin, red-tag the job, and escalate to the service manager, because a recovery is a multi-day period during which the water is both more attractive and less visible than usual. Nobody enters the water until the clarity gate at step 10 has passed.
Run a full panel with a titration kit, diluting the sample where the reading pins. Free chlorine by FAS-DPD, combined chlorine, pH, total alkalinity, calcium hardness, cyanuric acid, salt if applicable, and metals if the fill is well water or the plaster is already stained. Accept when every value is a number on the log, including a cyanuric acid figure. Wrong looks like a DPD sample that flashes pink and goes clear, which is not zero chlorine, it is chlorine high enough to bleach the indicator: dilute with known chlorine-free water and multiply back. Goggles and gloves for reagent handling, and never pipette by mouth. A recovery run without a cyanuric acid number is a recovery at unknown chlorine potency, and it is the most common reason one stalls.
Make the drain-versus-treat decision at the pad, on the numbers, before any chemical is bought. Cyanuric acid cannot be lowered except by dilution and the shock target scales with it, so a very high figure turns a treatable pool into a chemical sink. Accept a treat decision when the shock target step 7 derives is a volume the shop can genuinely hold twice a day for several days and the filter type can pass the load. Wrong looks like committing to treat at a cyanuric acid figure near or above 100 ppm with a cartridge filter, which blinds within hours. Where the decision is a partial drain, stop here and hand off to the drain and acid wash standard for the hydrostatic gate before any water leaves the pool; a shell that floats out of the ground is not a chemistry problem.
Remove gross debris and leaves before dosing, working from the deck. Leaf rake on a pole, then a leaf canister on the vacuum if the water will pass one. Accept when a rake pass returns essentially nothing on two consecutive sweeps. Wrong looks like dosing over a leaf bed, which consumes chlorine faster than the pump can circulate it and hides the floor from the later clarity gate. Watch the pole path for overhead conductors: a wet telescoping pole raised near a service drop is an electrocution, so carry it horizontal rather than shouldered.
Prepare the filter for a heavy load and plan to clean it repeatedly. Backwash a sand or DE filter to clear, recharge DE to the manufacturer's charge weight, and start a cartridge filter with clean elements and a spare set on the truck. Record the clean pressure. Accept when the gauge reads its clean baseline and return flow is full. Wrong looks like starting on the filter as found, because then you cannot tell a rising pressure from an already-high one. Open the air relief and confirm the vessel is at zero before loosening any lid clamp: a filter lid released under pressure leaves the vessel like a projectile.
Bring pH down to the low end of the range before the first shock dose. More of the free chlorine exists as hypochlorous acid at lower pH, so the same parts per million does more work. Accept a pH near 7.2 confirmed on a fresh sample. Wrong looks like acid poured straight into a skimmer or against return flow. Pre-dilute by adding acid to water, never water to acid, pour at arm's length downwind in goggles, face shield and acid gloves, and keep it away from any hypochlorite you are staging, because acid and hypochlorite in contact release chlorine gas.
Set the shock target from the measured cyanuric acid, and dose with unstabilized liquid chlorine only. The trade's working relationship is a shock target near 40 percent of measured cyanuric acid and a maintenance minimum near 7.5 percent; that follows from the hypochlorous acid equilibrium, not from a code, so record it as the shop's operating rule. Accept when a titration 30 minutes after the dose, pump running, reads at or above target. Wrong looks like reaching for trichlor or dichlor, which adds cyanuric acid and raises the target you are chasing. Pour from a marked measuring vessel below chest height, downwind, gloved and goggled, never back into stock.
Hold the shock level with twice-daily titration and re-dose, pump running continuously. Test morning and evening, re-dose to target every time. Accept a day when the evening reading is at or above target and the morning reading has not fallen below the maintenance minimum. Wrong looks like a morning reading at or near zero, which is not a failed program but an uncontrolled demand: re-dose to target, log the crash, and do not advance any gate that day. If two consecutive days show no reduction in demand, escalate to the service manager for a metals, phosphate or organic-load review rather than buying a third case of chlorine.
Brush the entire wetted surface daily and vacuum settled debris to waste, replacing water as you go. Walls, floor, steps, behind ladders, and the light niche lip. Accept when the brush has covered every square foot and the vacuum has lifted the settled grey layer. Wrong looks like brushing only the visible walls; algae survives in the shaded plaster of the deep end and reseeds. Vacuuming to waste drops the level, so run the fill hose as you go and never let the level fall below the skimmer throat: a pump that loses prime and runs dry destroys the seal and can crack the pot in minutes.
Release only on an overnight chlorine loss of 1.0 ppm or less plus a clarity check, then rebalance. Titrate at dusk once the sun is off the water, again at first light before it returns, and subtract. Use a 25 mL sample rather than 10 mL so each drop reads 0.2 ppm instead of 0.5 ppm, because at 0.5 ppm resolution you cannot distinguish a pass from a fail. Accept release when the loss is 1.0 ppm or less AND the main drain is distinctly visible from the deck. Wrong looks like blue water with a 4 ppm overnight loss, which is live algae eating chlorine faster than you can see it: the gate fails, the program continues, and the customer is told the day count moved. After release, let chlorine fall to normal before rebalancing alkalinity and calcium.
The record this produces
The recovery log, one line per visit day, carried across all days as a single record rather than as separate tickets. Fields per day: time of each test; free chlorine, combined chlorine and pH at each test; the cyanuric acid figure and the shock target derived from it, repeated on every line; product and quantity dosed; filter pressure at arrival and after any clean; brushing and vacuuming yes or no; water level action; the overnight loss with both readings printed; and the gate result, passed or failed, with the reason.
The service manager reads the gate column to authorize another day. The office reads the day count and dose quantities to bill against the agreed scope. Months later a recurring-algae callback is answered from the overnight loss on the release day: a release at 0.8 ppm loss is a different conversation from a release at 2.5 ppm because the customer wanted to swim on Saturday.
Worked pass: a 20,000 gallon plaster pool at 90 ppm cyanuric acid
Day 1. Barrier gate latches on release, no-swim notice signed. Panel: free chlorine 0 on a diluted sample, pH 7.8, alkalinity 110 ppm, calcium hardness 260 ppm, cyanuric acid 90 ppm, no metals. Filter is DE, so the drain-versus-treat gate resolves to treat. Shock target at 40 percent of 90 is 36 ppm; maintenance minimum at 7.5 percent is about 7 ppm. Debris out, filter backwashed and recharged, clean pressure 12 psi, acid to pH 7.2. First dose: at trade 12.5 percent liquid chlorine, one gallon raises 10,000 gallons by 12.5 ppm, so in 20,000 gallons one gallon buys 6.25 ppm and 36 ppm needs about 5.8 gallons. Titration at 30 minutes reads 35 ppm, accepted.
Day 2 morning, STEP 8 FAILS ITS ACCEPTANCE. Free chlorine reads 9 ppm, above the 7 ppm minimum but far below target, so demand is running hard. The stop rule is re-dose and do not advance the gate: 27 ppm back to target needs about 4.3 gallons. Evening reads 34 ppm. No release test is attempted on day 2, correctly, because the program has not shown a falling demand yet.
Day 3. Morning 21 ppm, re-dosed to 36. Water has gone green to grey-cloudy, which is dead algae, not a pass. Filter pressure has climbed from 12 to 20 psi, so the DE filter is backwashed and recharged mid-day and returns to 13 psi. Brushed and vacuumed to waste, hose running throughout.
Day 4. Morning 30 ppm. First overnight loss test: dusk 36.0 ppm on a 25 mL sample, first light 31.0 ppm, loss 5.0 ppm. Gate FAILS against the 1.0 ppm criterion. Customer notified the same morning that the release moved. The water is visually blue at this point, which is exactly the day a shop closes the ticket and earns the regreen.
Day 6. Dusk 36.0 ppm, first light 35.2 ppm, loss 0.8 ppm, which passes. Main drain distinctly visible from the deck, so the clarity half passes too. Released, chlorine allowed to drift down for two days before alkalinity and calcium are rebalanced, and the pool returns to route on day 8.
References
- CDC guidance on maintaining a disinfectant residual and on chlorine's reduced potency in the presence of cyanuric acid; the ratios used above are trade operating practice derived from that chemistry, not a published code figure.
- Test kit manufacturer documentation for FAS-DPD titration, including the sample volume that sets each drop's resolution and the dilution method for readings above range.
- Filter and pump manufacturer documentation for clean-pressure baseline, DE charge weight, and air relief before opening a pressure vessel.
- See related: the PoolService algae treatment procedure, the drain and acid wash standard for the hydrostatic gate when a drain is chosen, and the cloudy water diagnostic.