What is going on here?

[MeSue]

Hi,

I have a mystery with my pool and I'm hoping you all can help. We hadn't been swimming much because it has been raining almost every day. We were out of town Aug. 15-18 and the day we got back we went in the pool. So the 18th was the last time it had been used. That day, I noticed little tinges of green here and there--around the cove mostly--but it didn't feel slimy and it quickly dissipated just by swooshing it with my foot. I didn't brush. My chlorine tested at 6 FC and 0 CC, so I figured it was just leaf staining or pollen. Since then, the solar cover has been on and we haven't been swimming.

Yesterday I peeked under the cover as I was getting a water sample, and all over the bottom of the pool was green stuff. I tested the chlorine and again it was 6 FC with 0 CC. I noticed the low salt light on the SWG was blinking so I added a bag of salt and topped off with liquid chlorine to shock level (20) just in case my test is out of whack. I brushed to dissolve the salt and the pool clouded up from whatever was on the bottom. I switched the filter to continuous running and then later on in the evening, I switched the SWG to superchlorinate and I left the solar cover off. (I realize now that it messed up my chance of doing an overnight chlorine loss test by leaving the SWG on.)

Here are my test results from yesterday and this morning:

Yesterday (after adding salt)
FC - 6
CC - 0
Ph - 7.2
Salt - 2600
Borates - 50
TA - didn't check because it generally doesn't change that much
CYA - 70
Temp - 84

This morning the water was just a little cloudy, and there is still green in the areas where I could not brush, like under the ladder.
FC - 22
CC - 0
Ph - 7.6
Salt - 3200
TA - ???? (see below)
Temp - 82

Decided to test TA since I was planning to post here and I figured you'd want that, too. (Dang dark green reagent leaked and got all over my shirt--grrr.) The TA test results were very strange. Instead of going from green to purple and then magenta/red, this time it went from green to pale aqua blue, and then at drop 13 and higher it stayed at a pale orange color, like the color of very weak iced tea. What the heck??? Could it because the chlorine was so high?

Now I don't know if this could be a factor in all this but about 5-6 weeks ago, I reduced the pump run time from 8 hours a day to 7 as a test to see I could get by with less run time. It runs from 10 to 5 which is when the pool gets the most sun. It seemed to be doing fine until all this but I want you to have all the facts.

I bought all new test reagents at the beginning of this season, so I'm not using old testing stuff either.

I'm so confused! What do you all think is going on here? What should I do next?

 

[Butterfly]

You need to do the shock process as described in Pool School until you meet the three criteria that shows you are done. See red lines in my sig.

There could have been a combination of events to cause the problem, however, the most common is allowing the chlorine to drop too low or trying to maintain a chlorine level that is too low for the CYA level.

The CYA test is +/-15ish, so, the CYA could be higher which would require a higher FC level.

 

[MeSue]

Actually I was surprised the CYA tested that high. About a month ago, I topped it off to 70 and with all the rain splash-out we have had, I expected it to be lower. My chlorine level had been staying around 6 with 0 CCs, which should be fine. Anyway, will do the shock process starting tonight. My pool calculator app suggested 20 as shock level, but I see the chart in pool school says 28.

 

[chem geek]

You might have poor bottom circulation, especially if the returns are all pointed slightly upwards (perhaps for improved skimmer action). Pointing one or more downwards might help.

 

[MeSue]

That's what I was wondering. It only has one return and it has a poolskim attached so nothing to point. This is the first year with this pool and it is a little deeper than the old one. Anything else I can do to improve circulation at the bottom?

 

[JamesW]

It sounds like mustard algae
pool-school/mustard_algae

Re: TA

Total Alkalinity
High halogen level may change indicator reaction from green/red to blue/yellow; to prevent, add thiosulfate prior to testing.
http://www.taylortechnologies.com/produ ... KitID=2230

 

[MeSue]

It sounds like mustard algae
pool-school/mustard_algae

Ugh--it sure does. And since it had the solar cover on all week, it's not likely THAT much pollen could have got in. But it was only on the floor and cove, not the walls, which points to pollen. I don't know!

And if it was mustard algae, wouldn't I be since some CCs in my tests? I tested this morning, this afternoon, and this evening and always had zero CCs, and my TC level only dropped a small amount which seemed normal for having the cover off.

Shocked up to 26.5 tonight and ran out of liquid chlorine. I thought I had another jug but didn't. We'll see what happens in the morning.

(not trying to be argumentative... trying to understand)

Re: TA
Total Alkalinity
High halogen level may change indicator reaction from green/red to blue/yellow; to prevent, add thiosulfate prior to testing.
http://www.taylortechnologies.com/produ ... KitID=2230

Interesting. Halogen? is that bad? I thought it was just light bulbs. LOL I mean, do I need to do anything about it, or just go by when the color stops changing for the test. It's possible I just had some residue in the vial. I will have to test it again when all this shocking is done.

 

[chem geek]

And if it was mustard algae, wouldn't I be since some CCs in my tests? I tested this morning, this afternoon, and this evening and always had zero CCs, and my TC level only dropped a small amount which seemed normal for having the cover off.

The presence of algae does not necessarily result in CC. If there's a lot of algae and if chlorine is reacting with it and it's free floating so some gets in your sample, then you'll measure some CC. But for smaller amounts of algae or for algae that is settled and not in the general bulk water from which you take a sample, you may not register any CC.

Remember that yellow/mustard algae prefers shade so if you have the pool uncovered and find that it grows mostly on the shady side of the pool, then it's more likely to be yellow/mustard algae. If it instead just tends to settle in crevices where circulation deposits it, then it may be pollen.

If your return wasn't connected to the poolskim, I'd suggest pointing it diagonally downward to improve bottom circulation.

 

[MeSue]

Okay, so there was no overnight chlorine loss. I am at 27 FC this morning. Should I assume it's mustard algae and shock it up to 40 for 24 hours? That seems crazy high. I brushed and vacuumed yesterday and it looks pretty clear now as far as I can tell in the rain.

 

[JamesW]

It would probably be good insurance to go to mustard algae shock level, just to be sure. Alternatively, if the algae seems to be resolved, you could allow the FC to come down in stages. Perhaps 25 % of the CYA for a few days and then keep it at 15 % of the CYA for about a week. If the algae returns then definitely go to mustard shock level.

Also, "Halogen" just means chlorine or bromine.

 

[MeSue]

Thanks everyone! I have company coming this week and next so I am going to hold off on the mustard algae shock until all the company is done coming. In the meantime, I will keep the chlorine a little higher than I normally do and increase the filter run time.