Annually Green pool

[cschnurr]

I didn't want to hijack 65corvette's post, but I've had the same problem ever since I put the pool 4 years ago. Each year, I get the water balanced and things look great until end of July /early Aug, then my pool turns green, and I fight it for a month and a half with shock, but it never really clears so give up and close it for the winter.

I've never had any indication of Cl drop overnight and my water is actually reasonably clear until I brush the green/yellow deposits on the bottom. This year I thought that maybe it could be pollen (as shown in photos of other posts) as the deposits are on the bottom and sloped walls.
This year I kept and monitored my Cl to between 5 and 10 (SWG recommendation is 1-3) for the entire season just to make sure but I have the same issue.

My numbers are as measured on my Taylor K2005 test kit
TC=5
FC=5
CC=0
pH=7.8
TA=90
CH=200
CYA=70
Salt =2800 (SWG)

I have noticed that the deposits form within an hour of the pump/filter being turned on.
I vacuum them up and then backwash. But they do not seem to form when the pump is off.
Thinking the deposits could be algae in my filter I poured shock amount bleach direcly into the filter and let it sit for a day, but no change.

I plan on doing the following experiment.
Run pump and filter
Run pump in re-circulate position
Do not run pump.
Repeat above with the solar cover on to see if there is any difference in the 6 scenarios

This is complicated by the fact that my vacuum cleaner always gets hung up as the liner floats about 1/2" from the wall in one area of the deep end, so auto vacuuming is difficult. I have checked with the city and the water table in our location is far below pool depth. During the pool build in April/04, there was no evidence of any water source/spring. I have done the 'pail' test and found no evidence of a leak. So the source of the water is a mystery

I do have a couple questions.
1) I notice that the shock level for Mustard Algae is 34ppm. Wouldn't this damage the liner?

2)The water behind the liner has always concerned me, could it be a complicating factor?
There is a pool store that recommended some sort of electronic leak test for $150,
Would you recommend this?

I'm getting frustrated and to top it off, I don't think it is my methods as I maintained a neighbours 30 yr old vinyl pool that is in need of major upgrade, and thanks to what I've learned in this forum, it was very easy.

Any help you can provide would be great.

 

[JasonLion]

A leak seems likely. Algae growing behind the liner could be constantly reinfecting the pool.

 

[waste]

I haven't gotten to the other post yet (it's next on my list, literally ) but this is reminiscent of a thread at PF by Matt 4X4 about a strain of algae that had characteristics of mustard algae and occurs annually - it's a tough strain to kill! Shocking to 'mustard algae kill' level and maintaining it until the beast is dead works.

What I suggest is next season, come the end of July, take the pool to that same cl level before it blooms. Apparently this is fairly widespread but the cause is, as yet, unknown :x It always shows up at ~ the same time each year so there must be something that 'triggers' it - but I don't have enough data (nor time ) to do a regression analysis of this

If you'd like me to dig up the link to Matt's thread on PF, just ask - I think I can do it quickly with a key word search.

Best of luck with this beast! If I can help further - simply ask :-D

 

[cschnurr]

Thanks waste, based on your description, I was able to locate the post.
I think this is the one you are describing.
http://www.poolforum.com/pf2/showthread ... light=year

In post#32 of that thread, Richard refers to needing 1ppm HOCL and has a chart that indicates at CYA =70 (SWG), CL should be raised to 44, and thats if I lower my pH to 7.5.

Jason's pool calculator is telling me CL=34 for mustard algae.
His CYA vs. cl chart states 28 for SWG.

Using a Taylor K2005 test kit, I will need to dilute 8:1 in order to measure so high.
I don't think we'll be swimming anymore this season, so I can use this as a learning exercise for next year. I'd like to lower pH to 7.2 shock to 30 for 3 days. Then keep this for reference next year mid July.

Any idea if this will affect my liner?

Interestingly, when I had the pool on recirculate today, the sediment build up on the bottom was greatly reduced. I think this indicates to me that the algae likely very 'alive' in the filter sand, even if I backwash regularly.

 

[JasonLion]

Shocking to mustard algae shock level very rarely has any visible impact on the liner, though it is right on the edge of very slightly bleaching the liner. Going higher than that will almost always produce visible bleaching.

 

[cschnurr]

Thanks Jason,
Last night, I added enough Cl to increased to 25, and turned the chlorinator off.
This morning, no apparent drop. (Dilution 10:1)

This morning I added
-brushed the entire pool bottom, stairs, and crevices
-added Muriatic Acid to lower pH to 7.4-7.5, but I won't be able to verify because of high Cl.
-added 'clarifier' into the skimmer and some directly in the pool.
-more Cl which should raise it to 30ppm
I'm going to let it stay here for a couple days.

 

[duraleigh]

Carl,

It has been my experience that a 2:1 dilution for the OTO chlorine test is sorta' in the ball park, but still not very accurate.

3:1 is very inaccurate and anything greater than that is virtually useless.

Your 10:1 test results are, most likely, completely unreliable.

 

[Hotrod30]

I use to have troubles with algae starting in midsummer to closing time. This year I had no problems. Even the wife noticed how clear the pool was in August. I close after Labor Day.

Just my own opinion here but:

1) Your FC should be raised to between 6 to 7ppm when the pool water get above 84 degF.

2) Have you thought about adding borate (20 mule team) to the pool.



I added borate and salt (non-SWG pool) to my pool this year after reading about it on this forum and my pool has never been so clear; right till closing time. After openning shock (I won't say how high I go), the pool was never brought up to shock level again for the season. I also had the FC in the 6 to 7ppm range all season after getting the TF water testing kit from duraleigh. I use the test kit every-other-day for chlorine and PH and record the test and if we had rain (how much) and if the solar cover was taken off in the 2 day period. I also run my pump 24/7.


Like I said, my two cents.

 

[cschnurr]

Dave,
I use the Taylor K2005 test kit which is a DPD test, not OTO.
I guess I just assumed that the DPD test error is simply proportional to the dilution.

Eg,
If the undiluted measuring error is +\- 0.5 ppm, then
if I use 9 parts tap water to 1 part part pool water then the error will around +/- 4.5.
Is this valid?

Hotrod, I have not tried borates maybe next year.

 

[waste]

Carl, if you ask Dave real nice, he will send you the FAS/DPD test chems (I did it last year, the shipping was quick and it made my K- 2005 kit equivalent to the K-2006) 8)