Fighting Black Algea

[jimen]

So glad to have found these forums and appreciate all the info available to help pool owners!

We put in a 10,000 gallon SWG pool with Pebble Tech finish about 3 years ago (pic attached below post). We are first time pool owners and the builder wasn't great about education and care info. However, the pool has been doing fine, and we thought we had everything under control. We tested the water occasionally, had noticed some flakes a time or two and got some advice and chemicals from the local pool store and that went away. Basically things were okay until recently though we always struggled keeping the chemicals in balance. We've had a lot of rain this spring, the pool has run over a couple times and we've had to adjust the level and add chemicals, etc.

About 4-6 months ago, we noted a few brown-black spots had cropped up. We did some reading online, thought it might be dirt scale, and got especially vigilant about weekly brushing with nylon brush, testing the water, and maintaining the chemicals. This helped a few places, others not so much, and the spots seemed to be multiplying. Based on what we've read the last couple days, including the article here on TFP, we have determined we have black algae

We have the Taylor K-2006-SALT, DPD-FAS test kit but have also been having the pool place test the water to help us ensure we use the kit properly. The pool store’s test as taken today is attached (they said the Free Chlorine was actually 14 but their field only goes up to 9.9). But using our kit, we found the current levels to be:

Free Chlorine: 10.4
Combined Chlorine: 0
PH: Greater than 8
TA: 110
Calcium Hardness: 450
CYA: 40
Salt: 3090

We have not been shocking our pool up to now, as it didn’t seem to need it and we were told that a SWG would help with the need to do shock treatment. From what I read on TFP, we should have been doing that weekly. I think we better understand now too about the Chlorine/CYA ratio, versus targeting them as isolated figures which is what we have been doing (rather unsuccessfully).

Anyway, after reading the black algae page, it appears we need to do the SLAM process, and brush at least twice daily with stainless steel brushes. But the Chlorine/CYA Chart recommends a CYA level above 60. Should we raise the CYA level to 70 before staring the SLAM process? And have we missed any other steps that need to occur before we add the liquid chlorine?

Any advice/thoughts on how to proceed are appreciated, and thank you in advance!!

 

[Texas Splash]

Welcome to TFP! If you are convinced the spots you are seeing are from black algae, or any other algae for that matter, then yes - follow the SLAM Process. But do NOT increase the CYA at this time. Doing so would require more bleach (FC). So after you lower the pH to 7.2, increase the FC to 16 and maintain it until you pass all 3 SLAM criteria. Once you pass all 3 SLAM criteria, then you can increase the CYA to about 70 for your salt pool.

Now if you have any doubts about the stains being algae, you can also perform an Overnight Chlorine Loss Test. Once the SLAM is over, we can help you adjust all the other items tested based off of your Taylor testing.

 

[jimen]

Sadly, we are confident it is algae, definitely slimy and scraped off with a fingernail, and green when rubbed on a white sheet of paper. We will add the acid tonight to lower the PH and check tomorrow to see if it is at 7.2 then start the SLAM. Thank you for the quick reply!!

 

[jimen]

We added 5 cups of CYA yesterday and the PH today is still at 7.8. Should we add another 4-5 cups?

 

[cooltouch]

Jimen, I'm still kinda new here too, so consider my comment to be about equal parts question, but from what I understand, CYA isn't used to control the pH. It's used to keep the chlorine from being burned up too rapidly by sunlight. One of the problems inherent with CYA is it doesn't go away. About the only way to lower your CYA number is to drain off some of your pool, or to do it using some other method of water exchange. When I first came here, my pool's CYA was way too high. I ended up emptying almost half my pool to get the CYA back down to a reasonable level.

I use muriatic acid to regulate my pool's pH. I'm pretty sure that's what the old salts around here will recommend.

 

[mknauss]

We added 5 cups of CYA yesterday and the PH today is still at 7.8. Should we add another 4-5 cups?

Hopefully that is a typo -- you do not need to add any CYA. You use muriatic acid to lower your pH.

 

[jimen]

It was a typo, sorry still getting used to the abbreviations. We added 5 cups of muriatic acid yesterday and wondering if we should add the same today since the PH is still not down to 7.2.

 

[duraleigh]

What did it bring it down to?

 

[jimen]

@duraleigh it came down to 7.8.

 

[IceShadow]

Test your TA. Make sure PoolMath has that info as well. Then put in current and target pH and add acid as directed. Then wait 30 mins and retest.

 

[frogabog]

We have not been shocking our pool up to now, as it didn’t seem to need it and we were told that a SWG would help with the need to do shock treatment. From what I read on TFP, we should have been doing that weekly.

I just want to address this particular part about shocking weekly. TFP methods do not recommend shocking weekly/regularly, or actually at all ever. If your water chemistry is kept according to TFP recommendations, you will never need to shock, and most certainly not regularly as a preventative measure.

Should something go awry however, you will need to do the SLAM Process, which is a little bit like what you know of as "shocking", but it's a process rather than a one time application.

 

[jimen]

@IceShadow, thank you. TA is still 110--math says to add 27 oz, so we'll do that and test pH again tomorrow.

@frogabog roger that and thanks. i've done a lot of reading in the last few days, must have mixed up a couple articles. appreciate the feedback

 

[jimen]

Tonight the pH is back up to 8; TA is at 90.

I don't understand why are we having such a hard time bringing the pH down?

 

[Teald024]

I know your SLAM process is done now, but I wanted to address your question.
when you adjust the pH, you need to make sure to add the TA value as well. the amount of acid needed for a certain pH drop will vary based on TA.

The TA is on the high side and having a high TA will cause your pH to rise. Your pool surface should be old enough to not cause too much pH rise at this point.
if the FC level is above 10ppm, the pH test is not accurate any more. The test will falsely show a higher pH.
If you have a lot of water aeration like waterfalls or fountains, that can cause pH to rise as well.
As a final note, some pools just like to be at a higher pH and will rise faster.