What level of FC is OK for pool use? Algae, is that you???

[mackinac]

I've been reading Pool Forum and now TFP for a couple years now, my inground pool is in it's third year. I had a run in with black algae last year, but thought I had knocked it out... This year, I've got a green looking stain down between the pebbles in my pebbletec finish. I've shocked, polyquat60'd, brushed, and I can get rid of this. My water is clear, I've cleaned my cartridges out twice in the past 5 weeks. I finally got an FAS DPD test kit from this site, it arrived today... here are my numbers...

cya 80ppm
fc 11ppm
cc 0.5ppm
pH 7.0
TA 70ppm

residual chlorine from previous shock attempts... and I ignorantly added cya a few weeks ago hoping that "balancing" my water would help out...

so... I'm debating what level to shock to this time... my pump and filter have been running 24/7 for about 2 weeks now... salt is at 2700...

if I go for mustard/yellow algae level (45ppm FC with my CYA levels) I'm concerned how long it will take before we can safely use the pool. But the descriptions I've seen of mustard say it clouds out when brushed, this stuff doesn't budge, and it's not floating in the water.... I'm OK with dumping the 10 or 12 gallons of bleach in the pool if this is what it takes, but I'm not certain I've got it properly ID'd, and I'd hate to take the pool out of action for a week or so on a guess...

Any ideas, this stuff seems to be in shallow areas (tanning ledge, steps, swim out) and also in full sun...????????

My son has an underwater camera, I could post pics if that would help...

Mac

 

[frustratedpoolmom]

We love pics Are you sure what you had before was black algae? And this looks different? Does it do anything when you brush it?

80 is on the high end of the normal range for CYA with an SWG, so I wouldn't worry, it just means higher shock/fc levels.

I honestly don't know about swimming at shock levels....

With an algae outbreak, if you can hold the shock for 2 or 3 days, you'll probably kill anything in there and then it should drift down to normal levels while the filter clears out the dead stuff. But you are probably looking at a week, if I had to guess. Brush constantly the problem spots, especially while shocking.

Hope I helped, don't know if I did.

 

[chem geek]

Even with a pool at the yellow/mustard shock level that is roughly an FC of 60% of the CYA level, this is still just equivalent to a pool with around 1.5 ppm FC and no CYA. So somewhat similar to swimming in an indoor pool. Yes, the elasticity of your swimsuits will wear more quickly over a season of use, your skin will be more flaky and your hair more frizzy, but that's what my wife deals with every winter when she has to use an indoor pool at the community center that is at 2 ppm FC with no CYA. Just don't drink the water -- at least not quarts every day (not that you would!).

Now the above is not conventional wisdom, but that's how much I trust the chemistry.

Richard

 

[duraleigh]

Mac,

It sounds like you have simply suffered from underchlorination and the nature of your pool finish. Algae loves to hide in nooks and crannies and it sounds like you have some in your finish.

Keep your FC up around 10 or more (constantly) and BRUSH the algae spots with a bristle brush. That'll expose it to the FC and I believe it will clear your pool. Once your pool is algae-free, you could then lower FC.

As chem geek said, swim anytime you want.

 

[mackinac]

Thanks thus far... still no visible improvement. After the above tests yesterday, I dumped 3 jugs of ultra bleach in the pool, and let it run overnight.
Numbers this morning (chlorine only) were FC 22 and CC 0. Returned from work today, and numbers were FC 22.5 and CC 0.5. I guess my heaping spoonful wasn't exactly equal or something, but basically no change.

So, with no change does that mean that the FC is NOT being consumed killing algae (in other words, I think I've inferred from reading other posts that when the FC goes down, your still killing algae). But the discoloration remains. I just found the battery charger for the underwater camera, so I'll get some pics later.

Decided to dump 4 more jugs of ultra in after this test round. I'll post current results along with pics in a bit. Expect the FC will go up to somewhere in low to mid 30's...

Regarding using the pool, my son is complaining of some eye burn after swimming today, but that seems to be the extent of it...

More later, any guidance on the FC change vs. no change would be appreciated...

Mac

 

[duraleigh]

Mac,

Are you brushing? I would expect this will take a few days even if you brush twice daily.

And, yes, since you consumed no FC, you killed no algae. Doesn't mean it isn't in there, tho.

A pic might be helpful

 

[mackinac]

First, I've taken some pics, they should be viewable here:
http://i292.photobucket.com/albums/mm3/ ... ny0002.jpg
http://i292.photobucket.com/albums/mm3/ ... ny0004.jpg
http://i292.photobucket.com/albums/mm3/ ... ny0005.jpg

Also, my chlorine readings this morning:
FC 31.0
CC 0.5

Yes, I am brushing the areas at least twice a day with a nylon/stainless blend brush. Although I see some "dirt or dust" when I brush, with 2 dogs that doesn't surprise me, and the "algae" doesn't seem to budge.

Another FYI.... I put a new tail scrubber on the cleaner yesterday, this morning it is GONE!

Mac

 

[mackinac]

I think I've got it on the run...

visually looks diminished... test results:

FC 28
CC 0

I'm gonna add more bleach to crank it back up over 30 and keep at it...

Fingers and toes crossed...

Mac

 

[duraleigh]

Nice pics...very revealing. I think you're gonna have to keep your FC up around 6-8ppm, even with your SWG.

The algae looks firmly established within the rocks and it's gonna take brushing and a constant high residual of FC to keep it at bay.

 

[mackinac]

A follow up after a few days away. Literally, I had a three day business trip this week, so I left instructions with my teenage son (yeah I know...) to dose 2 jugs of ultra bleach and brush the pool twice a day. He lived up to his end of the deal, and I tested the water this morning...

FC = 30.0
CC = 0
pH = 8.2 (dosed muriatic to lower back to 7.0 target)

Assuming it has pretty much held this level, I've been hovering about 30 FC for 5 or 6 days now, and the algae remains. I was optimistic in one post that I thought it had diminished, but this morning with no sunlight or glare to cloud my view, it is apparent that I still have a significant amount remaining.

Time to crank it up a notch, I'm going for 45 ppm and try that for a few days...

If this doesn't do it, I may be looking at an acid wash...

Any other ideas out there??? Do the pics look like yellow, mustard, what?????

Thanks,

Mac

 

[JasonLion]

Be careful with the PH! The PH test can be wildly wrong when the FC level is that high. I think that it is likely that your PH is way too low right now that you have added acid. You can't use the PH test at all when FC is over about 20, and it is less precise when FC is between 10 and 20.

After five days at extreme FC levels any kind of algae will be dead. Unless the FC level was much lower while you were gone or your CYA level is actually far higher, there is no real chance that anything is still alive in there. Given you have pebbletec and not vinyl, you can really nuke it with chlorine if you want. But I don't think it is going to improve if it hasn't already.

I suspect that you may have staining rather than algae, though the pics do look rather like algae. You should try the standard stain checks, hold a Vitamin C tablet to one spot for 30 seconds and see if that spot changes, repeat with a trichlor tablet and see if that does anything.

 

[mackinac]

I tried the Vitamin C thing last week, and I rubbed it into the "stain". It did remove it, but I couldn't tell if that was from the friction or the Vitamin C. You say just hold it there, will it dissolve and that alone would prove a metal stain? I don't have any chlorine tabs, never used em and don't really want to invest in a bucket of them...

I "typically" added 1/2 to 1 gallon of muriatic a week prior to the shock action to maintain my pH levels, should I use the same while the FC is this high?

Let's assume it is staining, what is the preferred treatment for that on pebbletec???

 

[JasonLion]

When FC is really high you have to guess at the PH change to expect. Keep adding acid at about the same rate you always have and things will be fine for a while.

You can just place a vitamin C tablet and wait 30 seconds, no rubbing. The results will normally either be an obvious improvement or no effect. If the vitamin C helps, you should do an ascorbic acid treatment.

 

[CarlD]

One good thing is that with your finish if the pH drops too low it won't melt your liner--the big drawback of vinyl is sensitivity to low pH and very, very high FC--but you don't have that.

The other GOOD thing is that chlorine is far more effective at killing algae at low pH. In the 6's it's much more effective than in the high 7's (Chem_Geek is a whiz on this stuff and so are some other folks. I'm not--I just know the "ballpark" ranges). So if pH is a bit low don't QUITE rush to raise it too high.

BTW, a teen who is SO good about keeping up on the pool care? Get him the V-game he really wants, or give him the car for a date--something as a thank-you!

 

[mackinac]

Guess what????

Home from work tonight, I crushed about 10 tabs of Vit C and loaded into a sock. Rubbed it gently over the top step which was pretty discolored, and like magic the stain is gone.'

THIS IS NO ALGAE, IT IS METALS (see photos I posted above for a look at what a metal stain can look like on pebble tec).

So, now I'm off to pool school to learn what to do. Seems like ascorbic acid and a sequestrant is what is called for...

I'll certainly learn from this...

Mac