Mustard algae coming back?

[icoffey]

We recently bought a house with a highly shaded backyard and an onground vinyl pool - 57,000 L. Because I didn't know any better I was using chlorination pucks and was having the local pool store check my water weekly and things started out OK.

Then I noticed when I turned the pump on in the evening brown stuff was jetting out for the first couple of seconds. I assumed it was just dirt and was backwashing the filter... about 3 weeks ago I realized my pool was not getting enough chlorine with the "add a couple of pucks" strategy my pool store was advocating so I decided to switch to BBB which I'd found by this time.

At around the same time stains showed up... small clumps of yellowish-green on the liner. I thought it might be mustard algae so I decided I'd shock the pool.

My levels were

FC = 0
TC = 0
CC = 0.0
PH = 7.5
TA = 150
CH = na
CYA = 35
Temp 75ish

I cranked the FC level up to about 21-22ppm for three days and started brushing regularly. There seemed to be an improvement but the stains were returning a bit each day. So I added 100 ML of polyquat (per the jug) last Wednesday. The pool seemed to improve and the FC was holding steady overnight with no CC. The water looked clearer. There was a noticeable sediment on the bottom of the pool (dead algae?)

I allowed the FC to come back down and I've now since yesterday been working on lowering the TA with muriatic acid. My current levels:

FC = 6
TC = 6
CC = 0.0
PH = 7.5
TA = 120 (this seems odd, I only added 1L of 31.5 % muriatic acid I'm surprised it came down this much?)
CH = na
CYA = 35
Temp 80

The stains seem to be returning to the pool... did I do something wrong here? Should I reshock? Use more polyquat? I'm not sure how to proceed.

 

[UnderWaterVanya]

If you really have Mustard Algae - follow this process:

pool-school/mustard_algae

The crux of this is that you shock normally then after passing all the criteria really turn the screws on the stuff and go even higher for 24 hours (details in the link) and make sure that all items that go in the pool spend at least an hour in the pool at the high level shock. Lights get pulled out and scrubbed, ladders, etc. Floats go in, pool cleaners, heaters get circulated etc.

 

[icoffey]

I did do that, but went a step further and maintained the mustard algae shock level throughout the entire shock process for extra killing power plus an additional 24 hours after. Everything seemed fine but my FC hasn't even come back down to normal yet, it's not been low enough for me to add more bleach yet, but the algae seems to be returning again.

I'm wondering if I need to re-supershock or if I should be looking at a higher polyquat dose.. or or or.

 

[linen]

Welcome to tfp, icoffey

How are you getting your test values?

From your description, I would expect your cya level to be much higher, therefore raising the needed shocking FC level higher.

 

[duraleigh]

Identify the stains. organic or metal. Do you know how to test them?

 

[icoffey]

Interesting, I don't know how to test them no.

I just redid my levels w/ TF100 kit:
ph 7.2 (and aerating)
FC 4.5
CC 0.0
TC 4.5
TA 100
CYA 45 (ish, hard to tell in twilight!)
CH 230
Temp 78ish

 

[duraleigh]

If you can get a tri-chlor tab (ordinary swimming pool "puck") then hold it somewhere directly on the stain for about a minute. If the stain lightens noticeably, it is an organic stain. If it has no effect, it is probably a metal stain.

Confirm that by crushing up some cheap vitamin C tablets, put them in a sock and then hold the sock directly onto the stain for three minutes or so. If the stain lightens up noticeably it is a metals stain.

Post back your findings and we'll go from there.

 

[icoffey]

Ok finally got some daylight hours to play with. The test was inconclusive. The "staining" seems to be some sort of very very fine dust in patches on the liner, and whether I put a tri-chlor tab or a sock on it either way it gets disturbed and is brushed away... I left both in place a for a couple minutes to see if it had an effect in the area around the contact zone but nothing either way...

Not sure what this stuff is?

 

[linen]

It sounds like either algae or pollen/dirt.

If you haven't done a OCLT, that is what I would do next (I would probably bring it back up to shock level to do it).

 

[Butterfly]

Yep, I agree w/linen. Are you brushing the pool?

 

[icoffey]

Since the staining started I have been brushing, was everyday while shocking but have slowed down since... Under normal circumstances is daily brushing required?

I'll try the loss test tonight.

 

[linen]

If by normal, do you mean when not shocking? While shocking, brushing should be done at least once per day (more is better). During normal operation, brushing is very pool specific. If you have good circulation and maintain your FC level properly, then you may not have to brush as often. Slippery walls/floors are a sign you should be brushing more.

By the way...I rarely brush my pool

 

[icoffey]

I do mean when not shocking. It may be pollen, we have 5 pretty big (80') oak trees in our back yard not sure what they drop out of the sky as we just moved in. It's also very shady obviously.

Here's a picture of the type of staining I'm talking about, it was taken yesterday and is actually worse today because I didn't brush (was letting it build for the vitamin c test today).

 

[linen]

If you can brush it, it not metals...so no need to do the vitamin C test. It looks a bit like pollen to me...if you can snag a bit of it, see if it is slimy...if it is, then I would guess algae.

 

[icoffey]

And another pic

 

[chem geek]

If it is mostly in shady areas, then it's more likely to be yellow/mustard algae; if in sun and where circulation "settles" then it's more likely to be pollen. If you can carefully collect some and feel it or better yet look under a microscope, then that will be more definitive.