Mustard algae - first time infection

After 2 weeks of high heat (over 100 degrees), my pool is showing its first ever infestation of mustard algae. The pool water was at 88-91 degrees during the heat and has finally dropped to a reasonable 82 degrees, which is pretty standard for this time of year.

I keep brushing the sides down, but the algae keeps coming back. Here are my levels:

Free chlorine = 4.2ppm
total chlorine = 4.6ppm
Combined chlorine = 0.3ppm
pH = 7.8
Hardness = 240ppm
alkalinity = 88 ppm
cya = 75ppm
copper = 0.1ppm
Iron = 0.3ppm

I was told by the pool store (and this is one that doesn't try to sell you stuff - they're actually honest & helpful) that my chlorine is too high and may be part of the problem. I added - at their suggestion - a non chlorine shock and some polyquat algaecide.

Forgot to say this is an inground plaster pool of 30k gallons, sand filter.

Any comments or suggestions would be appreciated...

Handy,
At best, your pool store is uninformed. That's the nicest thing that can be said about the advice they gave you so I'll leave it at that.

It's good that you posted a full set of test results; that helps people help you.

The non-chlorine shock and polyquat might help but probably won't sure your infestation completely. To do that you need to bring your pool to shock levels of chorine; per the Best Guess chart, that's 20 ppm for your level of CYA. You need to keep the chlorine at or above that level until the algae is gone and your pool will keep that level of chlorine overnight. You need to test frequently (three times per day would be best) and keep adding chlorine to return the level to 20+ ppm.

Do you have your own test kit? If not, look for one that includes an FAS-DPD chlorine test. The PS-234 available from PoolSolutions is the best but a Taylor K-2006 will also serve you well.

Keep an eye on your pH as well. The chlorine will be more effective at a pH of 7.2 - 7.4.

Keep posting results and asking questions here. Many people will be happy to help you.

Best of luck,
Kurt

BEFORE you shock the pool - you have METALS in your water - it would be best if you get the metals OUT of your pool prior to shocking. Getting a metal sequesterant prior to shocking might be the best option.

Check out the metals forum and algae forum.

I'm not sure that's enough metal content to be any factor. Quite frankly, I've never seen posted on this forum the level where metals become problematic.

If it were my pool, I think I'd shock it to kill the algae and then deal with the metal issues if they appear.

Handy, that copper probably got there by adding something to your pool that had copper in it (at some point in time). Generally, I would discourage you from using anything with copper.

Thanks all. I have no idea how the metals got in there, but we had the pool redone about 2 years ago, and perhaps the decking folks dropped something in when they stained.

I assume the advice is to shock - with chlorine shock, but without stabilizer- household bleach, right? And the measurement is free chlorine (FC)?

Thanks for all your help! (Yes I have a test kit to use).

Yes, you're right on both counts. Let us know how it goes....

Janet

Another question: I see that some folks have stated they "cleaned the filter" after the algae was cleared up. I have a sand filter that was just changed in June. Do I need to change the sand again (I hope not).

You'll just need to backwash the filter.