mustard algae?

[gtm]

I did the ascorbic acid treatment about a month ago. While the chlorine was at zero, I had Polyquat-60 in. The chlorine was brought back up slowly, as the directions for the ascorbic acid treatment indicated. That was finished 2-3 weeks ago. Based on what I've read here, I'm pretty sure that the ascorbic acid and Polyquat-60 effects on the chlorine are long past.

The problem is that I can't get the chlorine to hold. For the past 2 weeks I've been losing 4-5 ppm per day, as opposed to the 1-2 ppm per day that is normal for my pool this time of year.

Seven days ago I decided that I must have given algae a chance to get started despite the Polyquat-60, so I started shocking. I've held the level over 16 ppm for seven days now with no change in the daily loss rate. Sorry, but I haven't checked for overnight loss as I've been low on reagent (should have more arriving from Duraleigh tomorrow), but there's no way that I can lose 5 ppm per day to the sun in February with a CYA of 50 ppm, is there?

I've just about decided that it must be mustard algae and am thinking of taking the shock level up to 30 ppm (as per the Pool Calculator). But before I did that I just wanted to see if there might be any other ideas about this. Perhaps something related to the ascorbic acid treatment?

Here are my current numbers:

pH 7.5
TA 80
CH 350
Borates 50
CYA 50
Temp 64
No CC observed during this whole process

Thanks, Gary

 

[duraleigh]

but there's no way that I can lose 5 ppm per day to the sun in February with a CYA of 50 ppm, is there?

No, I agree, that's too much loss.

Do you have any visible indication of mustard algae? It's not shy and typically shows up in pools that have been neglected for a period of time....that doesn't sound like your pool.

How are you chlorinating? Generally, how does your water look?

 

[JasonLion]

If the water is clear and there is no visible sign of algae, I would do an overnight FC loss test. As duraleigh said, daytime losses in that range seem unlikely, however the overnight loss test is much more definitive for the presence of algae. Measure the FC level in the evening, after the sun as set, and again first thing in the morning. If the morning test is within 0.5 of the evening test then there isn't any algae.

The amount of chlorine you lose during the day depends on several factors. Cold water and short days will reduce the amount of chlorine lost. On the other hand, high FC levels will increase the amount of chlorine lost, since the sunlight loss is always a percentage of the starting level. If you are losing 4 to 5 FC during the day when starting at say 7, that would be highly unusual. But if you are starting with FC around 16 to 20 then that is a much more reasonable rate of chlorine loss.

 

[gtm]

Thanks guys. I tried to post a reply earlier, but lost it somehow. If it appears out of the ether, please forgive any repetition.

Dave, the pool is crystal clear and no sign of algae. I've had mustard before, and have seen none of the signs, which is why I sent this question before assuming that. I'm using 10%, 2.5 gallon jugs from the local Mom and Pop PS. Been getting it from them since August, but I'm not starting to wonder if I'm getting bum chlorine. I'm wondering how long it sits around during the winter. But probably just being paranoid.

Jason, you're right, of course, that the overnight test needs to be done. I'll do that as soon as I get the reagent reload from duraleigh, probably tomorrow. I'll hold off until then.

Thanks again, Gary

 

[gtm]

Jason, you're right, of course, that the overnight test needs to be done. I'll do that as soon as I get the reagent reload from duraleigh, probably tomorrow. I'll hold off until then.

Jason was right, and thanks to him I've saved quite a bit of chlorine by not needlessly shocking for mustard algae. I'm still a little confused, though, and wanted to say what I found and see if there are any other thoughts on what's happening.

A day or so after my last message Duraleigh's troops came through with the much-needed ammo dump. It's great that these orders get processed so quickly! With a reloaded test kit I did the overnight test twice (Thu-Fri and again Fri-Sat). Both times the chlorine held overnight, as Jason predicted. I haven't added anything the past three days.

The chlorine loss during the day was 15 to 12 ppm on Friday, and 12 to 10 ppm on Saturday. I realize that this percentage loss is maybe not that large, but it's unusual for my pool. About 6 weeks ago I had the chlorine at similar levels prior to starting the ascorbic acid treatment, and was only losing just over 0.5 ppm per day.

It occurred to me that this higher loss rate would be consistent with a lower CYA level, so I tested that again on Saturday and found out that I'd dropped from 40-50 ppm to 20-30 ppm sometime in the past two weeks. I tested this several times, taking into account the temperature and mixing time concerns that have been discussed here recently. Also, I haven't drained and re-filled at all during this time, so dilution doesn't seem to be a factor.

Interestingly, over the same time period, my TA rose from 85 to 100 ppm. Again, I can't explain this based on anything I've added. I don't know if this is relevant, but it was the only other oddity in the tests. Maybe it's just a coincidence, but maybe it'll mean something to someone here.

At this point I've decided to keep the FC at the target level for a CYA of 50 ppm; i.e., assume that there was something weird with the test. I'll test again next Saturday, and if the CYA still shows 20-30, then I guess I'll accept the result and proceed accordingly.

I've read here about CYA "disappearing", especially over the winter in closed pools, so I'm not doubting that it's possible. Just a little nervous about doing the maintenance assuming that such a quick, unexplainable, change is correct.

Sorry for the length of this, but hopefully the facts might help someone educate me. I'd appreciate hearing any ideas you all might have.

Best regards, Gary

 

[duraleigh]

Hi, Gary,

I still can't quite figure this out.......

I did the overnight test twice (Thu-Fri and again Fri-Sat). Both times the chlorine held overnight, as Jason predicted. I haven't added anything the past three days.

The chlorine loss during the day was 15 to 12 ppm on Friday, and 12 to 10 ppm on Saturday. I realize that this percentage loss is maybe not that large, but it's unusual for my pool.

Are you calculating how much FC you are putting in and then testing to see if that's what you really got? Something is not right with these numbers. If you haven't added more FC, are you saying you added enough to get to 27+FC on Thursday.

Even then, a 12-15ppm FC loss in a pool with 20-30ppm CYA still isn't right. I'm at a loss to suggest where to go from here with your test numbers but something is not adding up right.

Meanwhile, If you see no mustard algae, you probably don't have it. From your overnite test, you shouldn't have any algae at all but it's difficult for sunlight alone to cause that kind of drop in your pool. The screen enclosure makes that much drop even less likely.

 

[gtm]

Hello Dave,

Sorry that I wasn't clear on the FC numbers. Let me try again. Please note that I have not added anything to the pool, including chlorine, since Wednesday. I didn't want to complicate the usage readings by having to adjust for what I'd added, and after hearing from you and Jason earlier I no longer really believed it was algae anyway.

Here are the FC results for the past 3 days (CC was zero everytime):

Thu pm - 15 ppm
Fri am - 15 ppm
Fri pm - 12 ppm
Sat am - 12 ppm
Sat pm - 10 ppm

When I say "am" and "pm", I mean just before dawn and just after sunset, respectively. I hope that makes more sense. Thanks for having a think about it for me.

Cheers, Gary

 

[duraleigh]

Got it! :-D That sure clears up my thnking. I'd say your pool is in very good shape.

 

[gtm]

I'd say your pool is in very good shape.

It is - thanks to all the folks here at TFP!

But I'm still curious about the daytime FC loss increasing from just over 0.5 ppm per day to 2-3 ppm per day. Even if I express it as a percentage of the FC level, as Jason mentioned, it's still more than what I've been seeing over the past 6 months that I've been taking care of the pool. Higher even, BTW, than I was seeing last August, which was at the height of UV exposure and usage time.

If I really have lost half my CYA sometime in the past two weeks, than that might explain it, but then I wonder about where it went. As I mentioned, I don't want to accept quite yet that the CYA is now 20-30 ppm and adjust my FC target accordingly. If it's wrong, and the CYA is really still in the 40-50 ppm range, then I'd be risking letting algae get started.

 

[duraleigh]

Gary,

Yeah, I'm not sure why it has changed....it should stay pretty consistent altho losing .5ppm, even with the screen (that's a big factor) seems unusually low. Generally, we see reports of 2-3ppm daily as a normal loss in a normal pool. With your screen, I would guess you should be about 1/2 that.

My best guess is there is just enough testing error in these tests to be off by a 1ppm or so and that you actually do have some organics in there. That said, keep in mind that only two things consume chlorine in a pool....the sun and organics. It would seem you have eliminated organics because of the two consecutive overnite tests but that whole loss to the sun seems just a little high.

My bet is it will stabilize in the near future but I'd test FC with the FAS/DPD test twice weekly for a couple of weeks.

Since you're dealing with the need for some pretty close accuracy, be sure to test the strength of your bleach by calcing the amount you neet to get to a certain ppm and then checking with the test to see if that's what you really got. If your chlorine is actually 95 instead of 10.5 (or whatever) it will obviously skew your results.

 

[gtm]

Thanks for the discussion, Dave. I'm just going to keep an eye on things for the next few weeks and see what happens. Depending on what I see I might chime in again. Thanks again ... Gary