Possible algae issue, overnight confusion, vacation planning

[markcw97]

Yesterday, I tested our AGP and discovered that the FC had mysteriously dropped to 1.5 and then realized that our over-the-edge SWG had stopped working -- I guess I should have been paying more attention. :-/

pH was 7.6, TA was 60, and CYA was 60. Based on the low FC, I assumed a high risk of algae and took action as soon as I could.

That evening, I bought and added 6 gallons of 6% bleach (WalMart brand Cleaning Bleach), which I calculate should have added 24.5 of FC, but I didn't verify that after adding. This morning, I checked it and surprisingly found it to be at 27, which would suggest some slight inaccuracy in testing, no FC loss during the day (it was cloudy) and basically no overnight FC loss? That doesn't add up to me.

I wasn't able to devote any time to it today other than testing (this pesky thing called "work" got in the way). This evening, I tested again after a mostly-cloudy day, and FC was down to 14.5.

A few questions/concerns:

1. Does FC drop more quickly in ppm when it starts higher (in other words, is FC drop more of a percentage or is it used up in ppm based on sun and organic matter?) I am guessing it's the ppm and that the drop of 12.5 today is due to algae, in spite of the pool appearing crystal clear.

2. We're getting ready to go on vacation Friday, so I don't have time to get a new SWG (I want a proper in-line one this time). We have a neighbor who is willing to check the skimmer basket and start the pool for us every night on a timer, and we can probably twist her arm to add bleach for us too. But testing the FC level would be asking too much of her, we feel. So we'd be shooting in the dark and also unable to vacuum/brush regularly.

3. Is there a benefit in going ABOVE shock level to compensate for the fact that we don't know how much it will lose daily and can't vacuum/brush? If so, what level is safe before we risk corroding the pump/filter or deteriorating the pool itself? Would raising CYA level a little help?

Tomorrow, I can spend more time monitoring and maintaining shock level, vacuuming, and brushing, but I fear that my efforts will be in vain when I leave the next day.

Any guidance on how best to tackle this to either eradicate the algae, or at least minimize the impact while we're gone -- would be MOST appreciated.


Thank you!

 

[mknauss]

1. Yes.
2. You will have to guess what FC loss each day. I would suggest 4 ppm. You might come home to a pool that needs a SLAM Process, or you might not!
3. DO NOT raise CYA! And no, no advantage to going above SLAM level for your CYA. Pretty much a waste of chlorine and potentially damaging to your liner.

Did you get your pH to 7.2 before you raised your FC? Would be good to do that if your FC is 10 or lower before you leave.

Take care.

 

[markcw97]

Thanks so much for your reply!

No, I didn't go back to the excellent sticky post here first to see that I needed to lower pH to 7.2 before I added a bunch of bleach. My bad. :-/

Can pH be lowered now, with the caveat that I won't be able to verify what I've lowered it to until I eventually let the FC drift back down to 10 or below?

Speaking of that, my thought was to try and maintain the pool close to Shock level over vacation... that's why I was wondering about ppm of FC loss when at a high level so I could estimate how much bleach to maintain Shock -- with or without extra FC loss due to possible algae.

Signed... Clueless in the Carolinas

 

[mknauss]

You reported a pH of 7.6 above. Was that a recent test? Does your pH normally rise or fall?

If recent and your pH normally rises, I would add sufficient acid to lower your pH from 7.6 to 7.2 before you leave. Be sure your current TA is in PoolMath when you do the calculation. That effects how much acid to add.

I would not suggest attempting to maintain SLAM level FC without testing. That could go terribly wrong.

 

[Jezza]

It's going to be pretty difficult to maintain a SLAM level of FC over vacation without someone being present to test and make chlorine additions.

Keeping your SWG ticking over while your away might help keep things at bay until you come home and deal with it properly.

 

[markcw97]

Thank you both!

Yeah, that was a recent pH test (same day I discovered dead SWG and FC of 1.5), and it used to tend to rise due to the SWG.

I will add the required acid to bring it back down, do an OCLT tonight, and hope it comes out as clean as the water appears already.

I won't try to maintain SLAM while we're gone, but adding 4ppm of bleach daily seems like it should allow the FC to drift down slowly and level off while we're gone, since we typically added about 2ppm using the SWG to maintain a normal FC level (5-8).