Seeing algae after salt cell outage

[MrDisco99]

So a few days ago I tested my water and there was ZERO chlorine measured. The salt cell was saying the salt level was too low. I even tried adding salt to bump it up but it did nothing. I took the cell and a water sample to my local shop to verify what was really going on. Turns out, as I suspected, the salt cell was bad and giving a faulty reading.

So I first tried cleaning the cell. Plugged it back in after and no change. My pH was high (7.8) so I dumped the acid water mixture I used to clean the cell into the pool. Not sure if that's relevant or not, but figured I'd mention it.

The cell seemed a bust so I ordered a new cell. While I waited I added a few gallons of bleach to the pool to hopefully get SOME chlorine back in there. I wasn't sure how much to add since I typically don't have to. I measured the next day and it still showed zero... so I guess it was't enough. The pH was 7.4.

All this time, the water seemed fine. It was clear to the bottom and didn't smell weird or anything.

Yesterday afternoon I got the new cell and installed it. I set it to super chlorinate and took out the shutoff timer so the filter and cell would run overnight.

This morning I had a look and I'm seeing green residue on the steps and the upper part of the vinyl at the deep end. It's not terrible, but it is visible. Looks like I didn't fix it in time after all. I took a measurement and I got a 6.5 TC, 0.5 CC, and back up to 7.6ish pH. I left it running like that for today and will check it again after work.

Did I do anything wrong (other than letting it run as long as I did with a bad cell)? Is there anything I should do now to clean this up or keep it from getting worse? Am I going to have to vacuum this stuff out?

Thanks in advance for any help. I'm still pretty new at this.

 

[Texas Splash]

Welcome! To remove algae, we at TFP follow the SLAM Process. To perform that SLAM, you need a proper test kit - either a TF-100 or Taylor K2006C. See Test Kits Compared. Also refer to the FC/CYA Levels and treat your pool as a non-salt pool for the SLAM Process and do everything on that page until you pass all 3 SLAM criteria. Use regular bleach or liquid pool chlorine to maintain the proper SLAM (FC) level 24/7. Once the SLAM is complete, you can revert back to the SWG. Let us know if you have any questions.

 

[MrDisco99]

Thanks... I already have a K2006C kit but it's been a while since I measured CYA. Last time I was showing around 60 though, which would suggest a SLAM level of 24. I have a 15,000gal pool. Sounds like I'm gonna be buying a lot of bleach today.

 

[Texas Splash]

 

[MrDisco99]

Haha!

OK so when I got home last night the water was still clear with the same few spots of algae which I brushed off. I decided I would do a measurement and OCLT just to check the status before SLAMing...

Last night at 9pm:

FC 9
CC 0.5
pH 7.7
CYA 60

I turned the salt cell off and added some HCl to bring the pH down and left the filter running overnight.

Today at 7:30am:

FC 8.5
CC less than 0.5 (pink was barely noticeable)
pH 7.4

There were a few spots on the walls, which I again brushed off. Numbers seem to indicate I'm ok, though, so what should I do? Should I still SLAM? Or at this point is it just a matter of vacuuming up what's in there? Apart from the bits on the walls, the water is clear.

If I do SLAM, with these numbers, how do I know I'm done? Just do it until the green bits go away?

 

[Texas Splash]

The OCLT is a great tool, but it's not 100% perfect. That's why we use the 3 SLAM criteria (clear water, CCs 0.5 or less, and passing the OCLT). So if you are sure the stuff you see is algae (brushes-up in clouds, or if captured feels slimy), then it's time to SLAM. If you need to SLAM, you simply need to:
1 - Lower pH to 7.2 (actually, at 7.4 you are probably ok. Your call if you wish to lower just a tad).
2 - Increase FC to 24 (SLAM level on the FC/CYA Levels based on your CYA).

Then follow the SLAM Process from there. Hope that helps.

 

[MrDisco99]

I came home to have a look at it on my lunch break. Looks clean but the Polaris has been running for the last couple hours. Looks just a little bit cloudy too. FC is down to 7.5 but the sun is pretty strong today.

I think I'm going to go ahead and SLAM if only to familiarize myself with the process, and just to make sure that whatever algae may be in there is gone. pH went up to 7.5 so I'm going to try to lower that and then I'll go get the bleach.

Thanks for the advice!

 

[MrDisco99]

I started the SLAM yesterday around noon. I bought 6 gallons of 10% Cl at Lowe's and I'm through 4 of them already.

I measured CYA again just because last time it was kinda dark and I got a reading of 70. I'm not a big fan of the CYA test process in the Taylor T2006 kit. Like... I can KINDA see the dot. I know it's there.

Anyway that gave me a shock level of 28. Yesterday afternoon I overdid it a bit with the Cl and got it up to 31.

This morning it was at 24. And I saw some green stuff on the steps and walls again. I thought I wasn't supposed to see new algae spots while I was at shock level?

Anyway, I've been brushing and testing every few hours. Thankfully it was overcast today so I didn't lose much FC. I haven't had to add nearly as much as I did yesterday, and for the most part the green stuff that was there this morning hasn't come back. I'm still seeing brown clouds when I brush the floor though.

I tested just now before dark and I'm right at 28. We'll see what it looks like in the morning.

 

[IceShadow]

Keep brushing, keep filtering. Kill the algae to brown, filter it out. If you have ladders, steps, light niches, make sure you’re brushing those too.

 

[MrDisco99]

I just did my morning check. FC 24.5, CC 0.5.

Bits of green on the walls again. I went ahead and brushed the whole pool. I'm realizing even if the vinyl looks clear blue, I'm still kicking up brown clouds when I brush, so I'm doing all of it each time.

Thanks for the tip about the ladder. I brushed it and big puffs of white came off it.

PoolMath told me to add half a gallon to get it to 28. I went ahead and poured the whole thing in anticipation of some of it getting killed by sunlight. Is that ok? I figured I'd rather have too much in there than not enough.

I can definitely see progress. It doesn't look nearly as green after brushing as it did yesterday.

 

[IceShadow]

Adding more than SLAM levels isn’t advisable. It isn’t going to help much as the higher the FC level the more it burns off. And too much can also damage things like vinyl liners. Better to test frequently if possible and keep it up at SLAM levels. Dropping below is ok if you can’t test super frequently.