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I have a hot tub that is built into my pool. The hot tub overflows into the pool for a sort of waterfall trickle effect. I've noticed recently these green spots starting to form :

What are they and how can I treat them? Are they an indication of something wrong with the water quality? I check it about every 3 weeks, and add chemicals as needed (usually requires PH down)

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The green stuff appears to be algae. It is most likely growing there because that area gets wet occasionally with the treated pool water but then is left exposed to the air without the water present.

The way to control that on most hot tubs attached to a pool would be to normally set the water diverter valves at the pool pump to circulate the pool water through the hot tub and then to the pool. Pools that I've had experience with will still permit some of the daily pool pump circulation to go to jets in the pool proper. If you keep the chemical balance in the pool correct the flow of treated water should control algae growth. (BTW I think only testing and adjusting your pool chemical state every three weeks is far too long of interval. This should be done every week so you can stay on top of things when climate conditions change).

With persistent growth like showing in your picture you may be faced with having to do a direct cleaning of that area after applying some algaecide. The chemicals may require selection as some types are designed for specific colors of algae (yellow, black, green, brown etc).

  • Hm, this seems unfortunate for me. Our hot tub drains slightly (into the pool) when the pump is shut off, which would explain the exposure. Unfortunately, we haven't been able to fix that yet. – ctote Oct 26 '15 at 5:12
  • one idea would be to try to remove those algae growth areas by sealing under the tiles. (silicon or some boat epoxy) Just don't know how good it will look. – Hightower Oct 26 '15 at 5:59

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