Black algae? Used wrong chemicals?

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Copernicu

Copernicu

Bronze Supporter
Jul 22, 2020
61
Phoenix, Arizona
I finally got my water back to blue (it was green), and now I have what looks like brown dirt on the bottom of my pool that won't sweep up. I discovered it recently, but I have no idea how long it's been there since I haven't used the pool much this year and also not much last year. Three people at two different pool stores think it's black algae. Below are two photos. The first is the stuff at the bottom of the pool. The second shows what I scraped off with a fingernail and put on a white piece of paper. .

Brushing as hard as I can with a nylon brush seems to have no result. I read that you can't use a wire brush on a fiberglass pool.

I'd like to get rid of this stuff. Also, I'm hoping I haven't messed up my pool after following the "expert" pool store recommendations. I found this site last night and ordered the TF-100 test kit this morning.

In case it's helpful, here are the results of Leslie's "AccuBlue" testing, and notes on what I've done so far.

7/14/2020
FC: .26
TC: 1.26
pH: 7.8
TA: 100
calcium: 229
CYA: 48
iron: 1
copper: .1
Phosphates: 410
TDS: 800
Notes: per pool store recommendations, I put in several pounds of powder chlorine, and then 1/2 a bottle of NoPHOS to get rid of the phosphates. They told me the phosphates were increasing algae growth and decreasing the effectiveness of the chlorine. I repeated this process twice. This helped, but the pool was still a bit greenish.

7/21/2020
FC: .65
TC: .86
pH: 7.9
TA: 99
calcium: 250
CYA: 48
iron: 0
copper: .2
Phosphates: 0
TDS: 600
Notes: per pool store recommendations, I put in about 3 pounds of dry acid. They also recommended 10 oz of chlorine. I decided to go "all out" and put in 6 pounds of powder chlorine. This cleared up the pool but I discovered the brown stuff on the bottom. Even thought this is when I discovered it, I really don't know how long it's been there.

7/22/2020
FC: 8.15
TC: 9.09
pH: 7.5
TA: 93
calcium: 273
CYA: 56
iron: .1
copper: .1
Phosphates: 19
TDS: 800
Note: now the goal was to get rid of what they told me was black algae. I put in a bottle of Black Algae Killer, and was told I'd need to follow up the next day with CuLator. I really did not like the idea of raising the copper in my pool but thought I'd follow the "expert" advice.

7/23/2020
FC: 1.97
TC: 2.52
pH: 7.4
TA: 92
calcium: 223
CYA: 52
iron: .1
copper: .3
Phosphates: 133
TDS: 950

And this is where I am now. Huge drop in FC, and big increase in phosphates and TDS, from yesterday to today. Copper went up but not as much as I feared.

Not sure what to do next. Based on what I read here, it sounds like I need to wait for the test kit. I bought a bunch of HDX Liquid Chlorine and figured I could start putting some in while I await the test kit but not sure how much.

Any suggestions on what to do would be greatly appreciated.



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I received my TF-100 kit and here are my results:

FC: 0
CH: 400
TA: 120
CYA: 0
pH (from K-1000): 7.8

I was really surprised by the CYA number. A few weeks ago, Leslie's AccuBlue said it was 52. I redid the test three times, and each time I could still see the black dot even when I filled the tube up to the top. Did the CYA really vanish?

The water looks blue and mostly clear. I have more of what appears to be black algae.

I thought I would SLAMming, but now I'm not sure how to proceed based on that CYA result.
 
Ok step one is done you have your test kit. It does not matter what Leslies told you your CYA was they are always wrong. Have you added CYA in the last 3 or 6 months?

In any case you dont have any according to the test kit we/trust you need to add 30ppm of CYA. Use the sock method. The start your SLAM.

The next question is you will need to scrape of that algae. I did not think that black algae could take hold in a fiberglass pool but in any case you will need to scrape that up. Go at it hard with the nylon brush and you are right, dont use a wire brush on fiberglass.

I am wondering if getting in the pool with a pressure washer might do the trick. I dont have any experience on fiberglass finishes so I dont know if that will damage the finish or not. I am sure some of the experts will chime in some ideas.
 
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Welcome to TFP :)

What was your chlorine source before you found us? Were you using 3 inch pucks or liquid chlorine? If you were using liquid you may have no CYA and if using Cal-hypo you also may not have any CYA..

I would just start your SLAM and brush daily and it will get rid of algae, black or otherwise.. Please do another CYA test just to make sure > pour it in a cup or another container so you can pour it back and forth 10 or 15 times... Your sure you add pool water to the bottom of the label and R-0013 CYA Reagent to the top of the label> mix for 30 seconds> sit for 30 seconds> mix again and pour back and forth..

If no CYA raise to 30 and go for SLAM, make sure to lower PH to 7.2 using 20% Baume Muriatic acid not the expensive dry acid they have been selling you... you can get it from Lowes https://www.lowes.com/pd/Crown-1-Gallon-Muriatic-Acid/3024039

Let us know if you have any questions :)
 
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Thank you @cowboycasey and @Katodude

My source of chlorine used to be 3" pucks,, plus powder chlorine for "shocking" from time to time. Since recently finding TFT, I have purchased liquid chlorine from Home Depot.

I re-did the CYA test (including pouring back and forth with a second container) and got the same result of zero.

I am going to buy some stabilizer this afternoon. According to Pool Math, it looks like I will need 6 pounds to get to 30 CYA. I don't know much will fit into a sock. I assume I should use multiple socks as needed to get the full 6 pounds in as soon as possible.

I had some leftover dry acid, so I added that today to get the pH down.

My plan is get to get CYA up to 30 and pH down to 7.2 (or at least 7.5) and then SLAM. In the meantime, I thought I'd add a gallon of liquid chlorine later today rather than let FC sit at zero.
 
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To be safe add half in the sock. Wait 48 hours after it dissolves and test again. You dont want to overshoot your CYA. Once the half is dissolved I would start SLAMing.

The key will be brushing. Brush, brush, and brush that algae to break up it protective layer.

I would brush, then test your FC (dont worry about CC for now), then bring your SLAM level up to 12.
 

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Update: I started the SLAM process this evening.

CYA got up to 30, and pH down to 7.5 (I was shooting for 7.2). There is more black algae. I brushed the pool thoroughly with a nylon brush (since the pool is fiberglass).

What chemicals other than FC should I be checking during SLAM?
 
At this point just check FC. As the algae disappears you can start checking for CC as well. But for now the key is getting and keeping the pool at SLAM level and brushing the heck out of that algae.
 
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Still SLAMming. The water clarity looks good, but the black algae is still there. Still losing a lot of FC. My pool logs show the FC numbers and what I've been adding.

I am concerned because the black algae does not come off during brushing. Is that normal? [It comes off if I scrape with a fingernail. Since my pool is fiberglass, I am using a nylon brush.]
 
So you dont need to be at full SLAM level but keep it higher than normal. If you CYA is still 30, I would keep the pool between 7-9 (Marty can probably give you a more precise number.) FC. You dont need to test multiple times a day since you are not slamming anymore. But daily should be good. Keep it high.

Now is also the time you get in the pool and really go after the remaining spots. Get a handheld scrub brush and get after them.
 
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@Katodude and @mknauss, thank you, I appreciate your help.

UPDATE: Good news: After 16 days and 63 gallons of liquid chlorine, I have successfully completed the SLAM process!

Not good news: There are still dark spots on the bottom of the pool. But I am not sure that they are black algae. There was previously black algae (that I could scrape with a fingernail), but I think it may be gone. The remaining black spots are in places where there are rough areas in the fiberglass, and in some cases actual gouges in the fiberglass. These spots appear to be resistant to additional brushing (including vigorous hand brushing in the pool).

1. Should I continue with the black algae protocol? Or should I consider these spots to be fiberglass imperfections and stop?

2. Either way, there are rough spots/gouges in the fiberglass. I"m guessing the only way to fix them is to redo the pool, which I'm further guessing is very expensive. How long can I wait to do that?

Suggestions?
 
I would say you can reduce the FC levels to target range. Gouges / rough areas of the fiberglass can be an issue but not much you can do until you decide to refinish. There are options of either re gel-coating or using EcoFinish. You might start investigating that.
 
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