Need quick confirmation that I'm dealing with iron

[PoolDoc]

I hadn't looked for your chart; I will. If it was there, it still is.

But, a small piece of trichlor will work fine. You can lower it into place with a thread. Just don't leave it there overnight, or anything like that.

[jenmenke]

OK. I put a tricolor tablet directly on top of a corner that had some orange starting to show and two hours later it was mostly gone. So that's algae, and not iron, right? So now what? My guess would be that I didn't keep the chlorine ppm high enough for long enough?

[PoolDoc]

You are correct.

Mustard algae can be eliminated by brushing + very high chlorine, and then continuing high chlorine and brushing after it all seems to be gone.

[jenmenke]

So what is "really high chlorine" for CYA 45 water temp 85?

[PoolDoc]

I'd probably start with 20 ppm (50% of CYA) and see if that works.

[jenmenke]

Ah! Now I get it: 50% of the CYA number is the shock level. thanks for saying that.

Here is an odd thing: I'd had the orange stuff on bottom and corners for a couple weeks before I posted here. Brushed, vacuumed, etc. Did one shock treatment, but only brought the chlorine to 15. Orange showed up again and then I posted, as I thought it might be iron. After doing your test with the trichlor tab in the corner where orange was, it all disappeared. No more evidence of orange. That was -- what -- 4 or 5 days ago? I have yet to see anything come back -- and I never shocked again.

Isn't that weird? I'm still waiting for it to re-appear... But don't you think I should wait before dumping all that chlorine in if I don't have to? The water looks perfect...

[PoolDoc]

50% of CYA is usually higher than you have to go.

But, mustard algae is tricky -- I'd recommend holding chlorine at a higher than normal level AND CONTINUING TO BRUSH regularly for at least a week after you think it's all gone.