Key takeaways
- The root cause of almost every Austin green pool is low free chlorine, usually from stretched service, high phosphates, or equipment failure.
- You cannot shock your way to clear water if the filter is dirty or the pump is not running; flow comes before chemicals.
- Multiple shock treatments over multiple days are often needed before the water starts clearing.
- Dead algae is white or grey, not green; a pool that turns grey and cloudy after shock is making progress.
- Phosphates must be addressed after the reclaim or the algae will return within weeks.
- One-time professional cleaning is usually faster and cheaper in total materials than a prolonged owner DIY recovery.
Austin context
In Austin & West Austin, green pools peak in June and July after the first real heat waves of the season, and again in September after late-summer storms. The combination of maximum UV, warm water, heavy bather load from holiday weekends, and common late-spring or post-vacation service gaps creates the conditions for rapid algae establishment. A pool that was borderline clear on Friday can be fully green by Sunday night after a heavy swim day and an afternoon storm.
West Austin pools with tree canopy face a secondary risk: high organic load from oak and cedar debris elevates phosphates, which are algae fertilizer. After clearing the algae, testing and treating phosphates is a necessary step to prevent rapid return. Pools near active lawn-care or landscaping operations may also pick up phosphate runoff through drain channels or splashback.
Assess the damage before starting
Stand at the deep end and look straight down. If you can see the main drain (typically 8-10 feet down in a standard pool), you may be able to handle recovery yourself with a few days of effort. If you cannot see 24 inches into the water or the pool is dark green or black-green, the algae load is heavy enough that professional service is likely faster and cheaper overall.
Also check the equipment before starting. Is the pump running? Is the filter pressure high? Is the skimmer pulling flow? A green pool with a non-functional pump or a packed filter will not recover no matter how much chlorine you add. Fix flow first.
- Light green or hazy: owner DIY recovery is reasonable with 2-4 days of effort.
- Medium green (visible floor but murky): borderline; professional service likely saves time.
- Dark green or black-green: professional one-time cleaning recommended.
- Any equipment issues (pump not priming, filter spiking): call a pro before adding chemicals.
Step 1: restore circulation
Clean the skimmer basket, the pump basket, and check filter pressure. If pressure is high, backwash (sand or DE) or rinse the cartridge before proceeding. You need maximum flow to support the recovery. Run the pump 24 hours a day throughout the recovery process.
If the pump will not prime after clearing baskets, stop. A pump air problem on top of a green pool compounds the recovery time and adds repair cost. Have a tech resolve the pump issue before starting the shock sequence.
Step 2: test and shock
Test free chlorine, pH, and alkalinity before adding anything. Adjust pH to 7.2-7.4 and alkalinity to 80-120 ppm first. In an acidic or low-alkalinity environment, chlorine is less stable even at high doses. Add liquid chlorine (sodium hypochlorite) to reach a shock level of 10-30 ppm free chlorine depending on the severity. Granular calcium hypochlorite also works but raises calcium hardness.
Add chlorine with the pump running and preferably in the evening to reduce UV degradation. Brush the walls, steps, and floor as you go to agitate the algae cells into suspension.
- Do not add stabilizer during a reclaim; you want chlorine to work aggressively, not be buffered.
- Add 1 ppm of sodium thiosulfate (dechlorinator) per 10 ppm of excess chlorine if you overshoot badly.
- Liquid chlorine (10-12 percent sodium hypochlorite) is the most common reclaim chemical; store and handle it away from acids and heat.
- Avoid copper-based algaecide during the reclaim; it stains plaster when copper is high and chlorine is high.
Step 3: brush and filter continuously
Brush walls, steps, and floor twice daily during the recovery. This breaks the algae biofilm and keeps cells in the water column where chlorine and the filter can do their work. Expect filter pressure to rise within 12-24 hours as dead cells load the media. Backwash or rinse as needed, sometimes twice a day on heavy reclaims.
The color progression is: dark green, lighter green, grey-green, cloudy white-grey, and finally clearing to blue. Each stage usually takes 12-24 hours with continuous filtration and correct chlorine maintenance. Stalling at grey-cloudy means either chlorine dropped, flow is insufficient, or phosphates are refueling regrowth.
Step 4: vacuum to waste
Once the water is cloudy blue or light grey, there will be a layer of dead algae on the floor. Do not vacuum through the filter; vacuum to waste (on a sand or DE filter, set multiport to waste; on a cartridge system, consult a tech since direct-to-waste is not always available). Vacuuming through the filter recirculates fines and can cloud the water again.
Vacuum slowly on a settled pool (at least 4-6 hours after the last brushing). Slow passes prevent stirring the material back up into the water column.
- Keep the pump running at normal speed, not reduced speed, during vacuuming.
- If visibility is not enough to see the floor, wait another 12 hours before vacuuming.
- After vacuuming to waste, you will lose 6-12 inches of water; top up with fresh water and retest chemistry.
Step 5: address phosphates
After the water clears, test phosphates. If they are above 500-800 ppb, treat with a lanthanum-based phosphate remover. Time the treatment after a fresh filter clean (phosphate remover clouds the water and loads the filter), and plan to backwash or rinse the filter again 24-48 hours later. Skipping this step is why pools go green again within two to three weeks of a successful reclaim.
Weekly service prevents phosphate buildup from reaching trigger levels in the first place by removing debris, organics, and diluting phosphate sources through consistent chemistry management.
When to schedule professional one-time cleaning
If you are unsure about any step, if the pool is too dark to assess, if equipment is not working, or if you simply do not have the time to run 24-hour pump cycles and brush twice daily for three to five days, a Austin Pool Bros one-time cleaning is the faster path. We assess the chemistry and phosphate situation, execute the shock sequence, manage filter cycling, and return for a follow-up vacuum. The cost is typically far less than a week of DIY materials plus potential equipment damage from poor-flow shock runs.
After a one-time cleaning, starting weekly service prevents the next green pool. Most of our green pool calls come from owners who are not on a regular plan.
Common mistakes
- Adding shock to a pool with a dirty filter and low flow, then wondering why it is still green three days later.
- Stopping the pump at night to save electricity during the recovery, which reverses progress.
- Vacuuming through the filter instead of to waste and recirculating dead algae back into the pool.
- Skipping phosphate treatment after a successful reclaim and having the pool go green again within weeks.
- Adding algaecide as a first step instead of restoring chlorine and flow.
Safe for owners
- Light green pools where the floor is still visible.
- Clearing baskets and cleaning the filter before starting recovery.
- Adding liquid chlorine and brushing twice daily during a multi-day reclaim.
- Vacuuming to waste on a sand or DE system once the floor is visible.
Call a pro
- Dark green or black-green pools where visibility is under 12 inches.
- Pools with equipment issues (pump not priming, filter not functioning).
- Phosphate testing and timed phosphate remover application.
- Full chemical assessment after reclaim including calcium and CYA.
- Pools where owner recovery has stalled after two or more days.
Why weekly care matters
Weekly service prevents nearly every green pool we see. The chemistry, brushing, and filter work done each visit remove the conditions that allow algae to establish. When a pool does go green between visits due to a storm, equipment failure, or heavy bather load, catching it early on the next weekly visit means a corrective treatment, not a multi-day recovery.
Common questions
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