Every pool service operator gets the green pool call. Sometimes it is a customer pool that turned green between visits. Sometimes it is a new prospect asking for a one-time fix before they sign for monthly service. Either way, the green pool is a profit opportunity if you handle it right, and a reputation problem if you handle it wrong. This is the operator playbook for green pool recovery in 2026. The SLAM protocol step by step, the chemistry math, when to drain instead of treat, and how to price the call.
TL;DR
- The SLAM method (Shock Level And Maintain) is the standard pool industry protocol for algae recovery
- Use 12.5% liquid chlorine only; never trichlor or dichlor because they add CYA and make the problem worse
- Plan 3 to 10 gallons of liquid chlorine over a 3 to 7 day recovery period for a typical residential pool
- Drain at least 50% if CYA is above 80 ppm; SLAMing is impractical and costly above that level
- Charge $250 to $700 for a residential green pool recovery, structured as chemical pass-through plus labor
- Always set written expectations on timeline; SLAM is not a same-day fix and customer surprise becomes a complaint
What turns a pool green
Algae blooms when free chlorine drops below the level needed to suppress growth, given the pool's CYA level. The most common causes: chlorinator off or empty for too long, heavy rain diluting chlorine, high bather load with not enough shock, salt cell stopped producing, or the CYA crept up to 80 to 100 ppm and the steady state chlorine is no longer effective.
Once algae starts, it self-perpetuates. The biofilm consumes chlorine faster than the system can produce it. The water turns visibly green within 24 to 48 hours of the chlorine residual hitting zero, and the longer it sits, the more chlorine demand the recovery will require.
The SLAM method explained
SLAM stands for Shock, Level, And Maintain. The protocol from Trouble Free Pool (the de facto standard reference in pool service) is to raise free chlorine to a specific target based on CYA level, hold it there with frequent additions until the algae is killed, and verify completion with a free chlorine loss overnight test plus a CC (combined chlorine) test.
The protocol uses 12.5% liquid chlorine (sodium hypochlorite) as the only chlorine source during recovery. Trichlor tablets are banned for SLAM because they add cyanuric acid, which raises the chlorine target and makes the recovery slower and more expensive. Dichlor and cal hypo have similar issues. Liquid chlorine adds zero CYA and works immediately.
“Trichlor tablets in a green pool recovery is like throwing dirt on a fire. Liquid only.”
Chlorine targets by CYA level
The free chlorine target during SLAM scales with the pool's cyanuric acid level. From the Trouble Free Pool chart:
- CYA 30 ppm: SLAM target 12 ppm free chlorine
- CYA 40 ppm: SLAM target 16 ppm
- CYA 50 ppm: SLAM target 20 ppm
- CYA 60 ppm: SLAM target 24 ppm
- CYA 70 ppm: SLAM target 28 ppm
- CYA 80 ppm: SLAM target 32 ppm
- CYA 90+ ppm: SLAM is impractical; drain water first
The target is held for the duration of the recovery, which is typically 3 to 7 days. Operators check free chlorine 2 to 4 times per day and re-dose to bring it back to target.
The 5 day recovery timeline
Day 0 (initial visit): full chemistry test. Brush the pool thoroughly to break up biofilm. Run filter 24/7. First chlorine dose to raise FC to SLAM target. Take a photo for the before record.
Day 1 to 2: chlorine demand is highest. Re-test and re-dose 3 to 4 times per day. The water often gets cloudier before it gets clearer (dead algae). Vacuum to waste if debris settles.
Day 3 to 4: water starts to clear. Chlorine holds longer between doses. Continue brushing and vacuuming. Clean filter (backwash sand, soak DE, hose cartridge) when pressure rises.
Day 5 to 7: water is clear. Run the SLAM completion tests: overnight chlorine loss (FC drops less than 1 ppm overnight) and CC under 0.5 ppm. If both pass, SLAM is complete and chlorine can return to normal range.
When to drain instead of SLAM
SLAM is impractical when CYA is above 80 to 90 ppm. The chlorine target becomes so high it is unsafe and uneconomical. The fix is partial drain and refill, which dilutes the CYA proportionally.
- CYA at 100 ppm: drain 50%, refill, CYA drops to ~50 ppm, then SLAM at the 20 ppm target
- CYA at 150 ppm: drain 60 to 70%, refill, CYA drops to ~50 to 60 ppm
- CYA above 200 ppm: full drain often makes more sense than partial; check plaster condition first
Other reasons to drain instead of SLAM: TDS above 5,000 ppm, calcium hardness above 600 ppm, severe staining that the SLAM will not address, or a plaster surface that needs an acid wash regardless.
Equipment that must run during recovery
The filter runs 24/7 for the full recovery. The pump usually needs to be at high speed (variable speed pump owners should bypass the normal program). Skimmer baskets get emptied daily because dead algae piles up. Filter cleaning happens 1 to 3 times during a SLAM as pressure rises.
If the pool has a salt cell, turn it off during SLAM. The high free chlorine target will not improve cell life, and you are doing all the chlorine work manually anyway.
What to charge for a green pool recovery
Green pool recovery pricing varies by severity and pool size. The 2026 residential range:
- Light algae (slight green tinge, less than 24 hours): $150 to $300 (1 to 2 visits plus chemicals)
- Moderate algae (clearly green, 2 to 5 days old): $300 to $500 (3 to 5 visits plus chemicals)
- Heavy algae (dark green, can't see the bottom, week+ old): $500 to $900 (5 to 7 visits, possible filter cleaning, more chemicals)
- Black or yellow algae: $400 to $1,000 (specialty algaecide plus extended SLAM)
- Recovery requiring drain: $400 to $800 plus water cost, plus SLAM after refill
Structure the bill as labor (your visits at $75 to $125 per hour) plus chemicals (cost plus 20 to 30% markup). Send a written estimate before starting. Customers who get surprised by the final bill leave bad reviews.
The customer conversation
Before you start a green pool recovery, the customer needs to know three things in writing. First, SLAM takes 3 to 7 days, not one visit. Second, the bill will be itemized labor plus chemicals at cost plus markup, expected range is $X to $Y. Third, the pool cannot be swum in during the recovery (free chlorine is too high).
Get this in writing via text or email before the first visit. The customer who agreed verbally and then complained about the bill is the customer who turns into a 1-star review. The customer who acknowledged the timeline and the estimate in writing is the customer who pays without drama.
Why SLAM recoveries fail
- Operator used trichlor instead of liquid chlorine, raising CYA and prolonging the SLAM indefinitely
- Filter not running 24/7, recirculation insufficient to distribute chlorine
- CYA was actually above 90 and SLAM was attempted anyway
- Stopped SLAM before passing the overnight chlorine loss test (algae still active, blooms back in 5 days)
- Brushed once on day 1 and never again. Biofilm survives in dead spots
Preventing the next green pool
After a recovery, the customer is in your debt. Use the moment to upsell what would have prevented it. Auto-chlorinator setup. Salt cell install or replacement. Weekly visits instead of biweekly. Higher CYA management to ride out summer rain events. Customers who just paid $600 for a green pool recovery will spend another $200 to never do it again.
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