Written for Utah water and Utah timing. Use it to sanity-check the pool before the visit, the quote, or the next panic text.
You walked outside, looked at your pool, and your stomach dropped, since yesterday it was blue and today it's a swamp. This is one of the most common panic-queries we see in Northern Utah, and it's almost always recoverable in under a week.
What caused it
Algae blooms in Utah pools have three common triggers, often combined.
- Chlorine drop. You stopped chlorinating, your stabilizer was too low, or a heat wave burned through your free chlorine faster than the dispenser could replace it. Most common cause overall.
- Pump failure or air-locked filter. Water stops moving and algae establishes in 24 to 48 hours. Common after a power outage or a pump-bearing failure.
- Phosphate spike. Recent landscape fertilizer use, lawn runoff, or a heavy storm can push phosphates over 500 ppb and feed algae fast.
What NOT to do
- Don't drain the pool in 90% of cases, since algae pools clear with chemistry and draining just adds calcium-spike risk on refill (Utah water is hard, remember).
- Don't dump a single dose of shock and walk away, because chlorine demand on a green pool is much higher than label dosing suggests.
- Don't shock without checking pH first, since chlorine is far less effective at pH above 7.8 and you'll waste product and time.
- Don't backwash before vacuuming dead algae to waste, since you'll just recirculate it into the filter.
The Utah-specific clear-water protocol
Day 1, reset chemistry and shock heavy
Test the water first, checking pH (target 7.2 for shock effectiveness), CYA (target 30 to 50 ppm, because higher CYA reduces shock effectiveness), calcium hardness, and phosphates if you have a kit. Adjust pH down to 7.2 with muriatic acid if needed. Shock with cal-hypo or liquid chlorine at 2x or 3x typical dose, so for a 15,000-gallon pool that's 3 to 4 lbs of cal-hypo or 2 to 3 gallons of 12.5% liquid chlorine. Brush the entire pool including walls, floor, behind ladders, and light niches, since algae loves shelter. Run the pump 24/7 starting now.
Day 2 to 3, hold high free chlorine and kill what's left
Test daily and hold free chlorine above 10 ppm until the water turns from green to cloudy-blue or cloudy-gray, which is the "dying algae" milestone. Add a quality algaecide on Day 2, preferably a copper-free polyquat, since Utah hard water doesn't need extra metals. Keep brushing twice daily.
Day 4 to 5, vacuum dead algae to waste
When water clarity reaches "cloudy gray" (typically Day 3 to 4), it's time to remove the dead algae mechanically. Vacuum to waste, not to filter, because dead algae will clog filters fast and rebroadcast spores. You'll lose water, so have a hose ready to refill while you work.
Day 5 to 7, filter, rebalance, lock it in
Clean the filter (cartridge soak, or sand backwash plus flocculant). Rebalance to pH 7.4 to 7.6, total alkalinity 80 to 120, calcium hardness 250 to 400, CYA 30 to 50, and free chlorine 2 to 4 ppm. If you're on a salt system, recalibrate cell percentage to maintain the new chlorine demand, since salt cells take 24 to 48 hours to catch up.
What's different about Utah pools
Two things matter here that don't matter as much in coastal markets.
- Hard water (18 to 24 grains/gallon). When you add muriatic acid to drop pH for the shock, you're also potentially shifting CSI (Calcium Saturation Index) into scaling territory. Watch calcium hardness, and if it's already above 400 ppm, use sodium bisulfate instead of muriatic for pH adjustment.
- Altitude UV. Once you've cleared the pool, your CYA needs to be on the higher end of the safe range (45 to 55 ppm) to protect new chlorine from burning off in our intense sun.
When to call a pro
Most green pools clear with the protocol above over 5 to 7 days. Call us if it's been 5+ days and you're still cloudy with no improvement, if you see solid sludge on the bottom and can't see the steps, if your pump or filter is acting up (an algae cycle is hard on equipment), or if you just don't want to deal with it. Green-to-clean is $499 to $899 flat with a 30-day algae return guarantee.