New Thread with my results of first test

[PoolDoc]

Mustard algae will re-appear in areas where you've brushed or wiped it off. It is usually on the shady side of the pool, and will appear on vertical surfaces.

[Watermom]

I also think if it was mustard algae you would have probably lost more chlorine today than just 1.5ppm.

[PoolDoc]

Not necessarily, in the early stages.

[Watermom]

Ok. Didn't know that.

[Tom.B]

While I am not sure it's on the vertical sides, it's certainly on the angled sides. However, it's not in a shady area or any real area in particular. It's spread evenly throughout. There are some green/yellow spots on the stairs, but that's all I can see in the way of concentrations.

[Tom.B]

Mustard algae will re-appear in areas where you've brushed or wiped it off. It is usually on the shady side of the pool, and will appear on vertical surfaces.

Is there any way to know for sure what algae I have?

[BigDave]

If it's yellow-ish (brown-harvest-yellow-chartreuse), it lays on the bottom and brushes up easily then returns, and is resistant to chlorine, I'd call it mustard algae.

[PoolDoc]

Is there any way to know for sure what algae I have?

Not really. It's not a species of algae; just a 'behavior' of some algal biofilms. Some years ago, I spent quite a few hours chatting with a senior researcher at Buckman Labs (inventor of polyquat). He told me that every single case of algae he'd studied, including samples from his home pool, involved more than 10 species of algae AND bacteria.

But Dave's description of the 'behavior' is accurate, with the addition that it's (a) often found on the bottom AND sides, and (b) typically is first found in shaded areas of the pool. It *will* 'bloom' and turn the entire pool green if not controlled.

[Tom.B]

Okay then... I suppose that I have it then. I guess I will read about it here and see what I can do about it.

[PoolDoc]

Mustard algae options:

1. Run chlorine levels at the 'algae' or 'shock' level continuously -- see http://pool9.net/cl-cya/ -- and brush a lot.

2. Run normal chlorine levels + maintain phosphate levels below 125 ppb (0.125 ppm).

3. Use lots and lots of copper, turn everyone's hair green, and stain the pool.

I'd recommend #1 first, especially if you've never had mustard algae before. If your pool is not one of the not-so-lucky ones prone to mustard algae, it may stay gone after you've cleaned it up.

But if you find you're struggling to keep it away, we can look at option #2. However this requires managing phosphate additions to your pool from multiple potential sources, including the fill water.