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Green water / high phosphates


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Hi everyone,

New here. I had a brand new Arctic Spa hot tub delivered about 3 weeks ago. It has an onzen system and was great for the first few weeks.

I removed the cover a few days ago to find green water. Called Arctic and they said to bring in some water to test.

Turns out I had phosphates (1549 ppb) and low PH. I was told to balance the PH and then use a No Phos chemical.

Did that, and with the No Phos, I got a really gross cottage cheese looking foam on top. Scooped it out and let it settle. Rinsed out the filters that were brown after only 3 weeks. Please keep in mind it is just 2 people that go in this hot tub and we've been in only a handful of times.

A couple of days later, water cleared and looked great. Levels were good. So I used the non chlorine oxidizer as I am supposed to once a week as I wanted to use it tonight. After the 20 minute cycle of the jets for Spa Boss Spa Shock, i looked out the water was green again.

The filters were brown again (one brand new filter) and there seemed to be a orangey dust in the water. Also, the PH plummeted. 

I called Arctic and am going to do another water test tomorrow, but just wondering what the heck is happening.

Any thoughts? I'd really rather not drain and fill after less than a month of ownership!

Thanks in advance.

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Without a full set of test results it's impossible to say what might be going on. Low pH is the red flag that stands out to me since phosphates are often a non issue. How low WAS you pH? Was the green water a clear emerald green (indicating copper) or a cloudy green (indicating algae)?

If the green water was caused by algae then it means the sanitizer levels were low and the tub was exposed to sunlight (necessary for the growth of green algae) which is unlikely in a tub kept covered.

Phosphate removers are Lanthanum (a rare earth metal) salts that work by causing phosphate to precipitate out as Lanthanum phosphate, which will cloud the water and eventually get filtered out. They create more problems than they sovle, IMHO. This explains the foam and the filter problem. However, there are better ways to deal with algae, IMHO, if that is what is causing the green water.  Phosphates are algae food and could be partially responsible for algae blooms but maintaining proper sanitizer levels and using a borate additive are effective ways of dealing with them and removing them only work when phosphate is the limiting factor in algae growth. Often it is not. However, it is a limiting factor that can be tested. and dealt with chemically. The other limiting factors are nitrites and nitrates, which can be tested but the only way to lower them  is by draining and refilling with water that does not contain nitrite/nitrate so there is no product that you can be $old to remove them. To give a real life example, my own pool and attached spa have phosphate levels of over 1000 ppb (essentially off the charts), has been that way for about 15 years, is exposed to full Florida sun, and has not had an algae outbreak in that time, including a 3 week vacation where the pool and spa were shocked and then turned off (and left uncovered and exposed to the sun) When I returned the water was still clear with no algae so I just shocked again once I turned on the pumps. I do run 50 ppm borate, which is an effective algaecide and preventative, in addition to its other benefits.

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