50 Causes of Swimming Pool Algae

dog-days-of-summer-2Currently, the Dog Days of Summer Sale is running here at In The Swim, which reminds me of an old phrase – the “algae days of summer“.

It’s the time of year algae has been waiting for. As water temperatures soar into the 80’s, your sanitizer struggles to keep up – ideal conditions for algae.

But there are other causes of swimming pool algae. So many in fact, that I’ve curated a list of what causes algae to grow in pools. In most cases, it’s not just one factor, but a combination of many…

What Causes Pool Algae?

Water Chemistry Problems

  1. Low free chlorine levels, below 1.0 ppm
  2. High combined chlorine levels, above 0.3 ppm
  3. High pH levels, rising above 7.6
  4. Low calcium levels, below 150 ppm
  5. Low alkalinity levels, below 70 ppm
  6. Low cyanuric acid levels, below 20 ppm
  7. High cyanuric acid levels, above 100 ppm
  8. Very high total dissolved solids, over 10000 ppm
  9. Never brushing your pool; ≈ weekly
  10. Never diluting the water; ≈ annually
  11. Not shocking the pool enough; ≈ monthly
  12. Not testing and balancing the water enough; ≈ weekly

    Pool Water Contamination

  13. Dead remains of previous algae blooms
  14. High levels of dissolved carbon dioxide
  15. High levels of nitrates or nitrites
  16. High levels of phosphates
  17. High levels of bacteria
  18. High levels of ammonia
  19. Dirty pool, lots of leaves, debris
  20. Heavy swimmer use, bodily wastes
  21. Mulch leaking in or blowing into pool
  22. Fertilizers carried in from rain or wind
  23. Run-off from nearby lawn or planters
  24. Sap and pollen from overhanging trees
  25. Urban pollution from cars and planes

    Equipment Problems

  26. Pump is overheating and cycling on/off
  27. Pump is too large for the pool filter
  28. Pump impeller is clogged or broken
  29. Leaking or low water levels, drawing air
  30. Stuck skimmer weirs, drawing air
  31. Air leak before pump, drawing air
  32. Poor circulation in a large pool
  33. Filter is too small for pool size or pump
  34. Filter cartridge not seated properly, or missing parts
  35. Filter cartridge or sand needs replacement
  36. Filter not running long enough daily
  37. Multiport valve is recirculating or bypassing filter
  38. Suction or return valves are closed
  39. Salt chlorinator cell needs cleaning
  40. Salt chlorinator cell needs replacement
  41. Salt level in pool is too low
  42. Tablet chlorinator is clogged
  43. Tablet chlorinator is air locked

    Other Problems…

  44. Rough concrete pool surfaces
  45. Gravel, plants or fish (!) in the pool
  46. High water temperature, over 80° F
  47. All day sun exposure, over 8 hrs daily
  48. History of persistent algae every spring and summer
  49. Dogs, ducks or other animals using the pool regularly
  50. Non-pool items in pool; furniture, bicycles, skateboards, shoes, fruit…

pug-in-poolIt’s often not just one thing that causes pool algae to bloom, but a combination of factors that come into play.

To sum it all up, keep your water balanced and sanitized, make sure your filtration and circulation is optimal, and keep contaminants away from your pool. Visit our Algaecide section for targeted treatments.

Davy Merino
InTheSwim Blog Editor



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