CYA is too high? Black Algae?

[spequigney]

Moved from here.
I'm dealing with high CYA issues so I've been keeping the chlorine level high. Background - I'm not a newbie, but call me a rookie since this is my first year managing my wife's pool and I have posted previously. She had terrible problems last year with cloudy water, some green algae on pool bottom, and an inability to hold chlorine. She followed pool store methodologies and I convinced her to allow me to manage it this year. We started the year with Silkguard tablets but stopped using them a few weeks ago. The good news is the pool has been crystal clear this whole year and no apparent issues from high chlorine levels when swimming with FC levels up to 8.2.
Readings from today - FC 12, pH 7.6, TA 110, CH 280, CYA 100. We have been having a problem I saw discussed on the forums here - black gunk in the skimmer above the water line. We use floating duck thermometers and when they get sucked into the skimmer there is a black ring at surface level. I bumped the chlorine up because I noticed some black spots in a corner in the shallow end, they are now gone.
I assume that at least part of the reason why CYA is so high is use of Silkguard tabs from opening at end of April into July. Removing and replacing water is not a practical option - the alternative is keep FC high and do better next year (CYA was 50 at opening). So I think I have a handle on that.
What I'd like feedback on is the black gunk, if that is black algae. Lots of post on that here.

 

[Texas Splash]

The black you are seeing may be two different things. You mentioned some of it above the waterline in the skimmer which sounds more like a scum line. Often times those are just oils and junk that gather in a corner or area and put that black coating at the waterline. I use a Magic Eraser on those. Then you mentioned some black spots in the shallow end that are now gone. I suspect those were just regular algae, because if they were truly Black Algae spots, they would probably not just disappear on its own.

Overall it sounds as if the reliance on chlorine tabs/pucks is what is your girlfriend's biggest problem. Pucks are fine for short-term use and when you know the CYA is low enough to handle it, otherwise you/she need to stick to liquid chlorine or regular bleach for the FC. Always keep the FC and CYA balanced as noted on the FC/CYA Levels to avoid algae. Hope that helps.

 

[spequigney]

Thank you - definitely agree about it being a scum line, used a Magic Eraser (Mr. Clean is the brand btw) and got it all off, now going to buy another and leave it in there. I've been using the Pool Math app and find it quite valuable - I can log not only levels but what chemicals go in, when I brush, when the filters are cleaned, even notes for something else I may want to note (like days when I find critters in the skimmer). Highly recommend.

 

[spequigney]

So here's a disappointing update - I have a couple of algae spots, green as in attached picture. I included a picture of my drains 8' down in the deep end to show how crystal clear the water is. Here are my readings: FC 7.6, CC 0.2, pH 7.6, TA 100, CYA 87, water temp has been upper 80s but now mid 80s due to a great deal of rain we got from hurricane remnants blowing through. I had my submersible pump running nearly the whole time so the skimmer would function properly. Filters were cleaned 8/1, it runs on high each night 12-6AM and while I cleaned out debris, runs on low all other times. I've studied and read enough on here to know what's coming but still welcome comments.

Scum line issue resolved. I brushed the waterline 8/2 and a good bit of the rest of the pool was brushed while cleaning out debris - which was not a substantial amount, took me around a half hour.

 

[Texas Splash]

Great shot of the drains and the water looks great. Unfortunately, that green spot is a concern. If it's algae as we suspect, a SLAM Process would be in order, but with clear water hopefully the SLAM will be completed in good time. I suspect what may have been part of the problem is the elevated CYA level. You posted a CYA of 87, but with the K-2006 we round up or down, and in this case it would be at least 90. You might test the CYA one more time to be sure after all the storm water exchanges, but once you confirm the CYA, go to the FC/CYA Levels and elevate the FC to SLAM level. Before you elevate the FC, be sure to lower the pH to about 7.2. Brush well during the SLAM Process and hopefully you'll get through that SLAM in good order.

 

[spequigney]

You are right about the K-2006, I kind of fudge that so 90 it is. Last time the pool store measured it was 92 - and they say that is fine. There may be a few laughs at my expense but after posting I went out, grabbed a chlorine tablet, put on my dive mask rubbed spots that looked like algae, then let it sit on the big one for a while. I'll next work on getting the pH down.

 

[spequigney]

Feedback indicates it is mustard algae - two more spots this morning with FC 10.5 CC 0.5. Put chlorine tablet fragments on each while I investigate further (including this post). Word is this type of algae is rare but more importantly, resistant to chlorine.

 

[spequigney]

Took a trip to the pool store this morning - they measured my CYA at 107 with a nice little green check by it, meaning they don't consider that a problem. I'm no longer sure what kind of algae keeps showing up in this one section of the pool - I put my duck chlorinator in front of the inlet in this part of the pool, tying it in place, and I place chlorine tablet fragments on top when they show up. They then disappear and usually reappear the next day, perhaps fewer in number but I'm drawing no conclusions. We have about five weeks left in the season so I may just ride it out since the water remains crystal clear, following the FC/CYA chart levels. I'll then attack the CYA levels over the winter via dilution.

 

[spequigney]

Update - was introduced to the issue of phosphates, my wife's pool store does not test for them. Ended up using Phos-out then clarifier, as testing showed it to be >2300ppb and I decided it was worthwhile to get it below 1000ppb which I did. I still get a few algae spots in the area of lowest circulation, keeping FC at 9-11 (CYA still over 100 so I know that is not a match). pH kept at 7.4-7.5, TA 80-90. Here's the interesting thing - since the phosphate removal was done there is no more black gunk in the skimmer. I keep the magic eraser handy but have not needed to use it. We had for some time noticed a film on top of the water in the skimmer, most noticeable with the pump on low - no longer. Pool to be closed three weeks from tomorrow so I'm not going to SLAM, over the winter will get enough water out so CYA is under 50 and go liquid chlorine only next year.