Black algae treatment in progress - strategy help needed.

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Dipper

Dipper

0
Jun 17, 2014
8
Austin, TX
I'm in the process of treating a black algae infestation. I've been lax and lucky for the previous 6 summers but lost this year to black algae and am now a convert to TFP methods and test kits. Thank you for being here. I've read everything I can on this site about black algae and think I understand the principles but am not sure how much effort or whether I want to put more effort into this old pool that came with the house. I need some feedback from some experts. Rainwater harvesting in my pool is starting to look appealing. Maybe a Koi pond? I would really like a "natural swimming pool" - 1/2 for human and 1/2 Koi pond.

OK - latest tests in 1/2 the pool volume (estimate 7500 gal of 15,000 gal)
CYA 70
TA 90
FC 21
CC <1
pH 7.8
CH 700

The black algae is covering a lot of the bottom, there are some rough areas in the plaster where the algae has taken up residence plus the blue-green spots on other areas of the pool. The rough areas are from some ignorant person, who shall remain nameless, putting trichlor pucks in the pool during the winter for passive chlorination. Well that wasn't good for the plaster but it appears still intact.

I drained the pool to about half with the idea that I will be diluting the CYA, I find it easier to scrub entire pool bottom, and I need less bleach. However, mixing chemicals is an issue somewhat since I can't use filtration until I fill the pool. I'm finding scrubbing the pool bottom with the 4 inch stainless brush and the foot long stainless brush on a pole very difficult and inefficient. When the FC was lower I felt more comfortable scrubbing the plaster up close, with the 4 inch stainless brush in my hand, wearing snorkeling gear and weights.

I notice that the black algae is fading as the bleach and scrubbing is working but I don't know how far to go before I fill up the pool again. Pictures would be best, I know.

What should I do at this point?
How do I become a better scrubber?
Should I bleach and scrub until I see NO evidence of even dead algae (gray colored)? Bleach until the plaster is white again?
Should I rent a power washer and work on the plaster?
Do I scrub the plaster with trichlor pucks?
What do I do with the cartridge filter or will the higher FC levels sanitize that also.
Is there any hope? or should I give up?

Other info and questions:
The main drain is closed because of a major leak in the line. I removed the plate because debris were collecting under the plate and consuming FC? Can a main drain plate cover be closed better?
Debris are also collecting behind the light. Can this be closed without debris collecting there either? The light went out again and I don't use it much anyway - it just draws bugs to the pool.

Thank you.
 
Welcome Dipper.

You need to fill the pool and get the filter running. Run a full battery of test and post them up here. Start SLAM'ing the pool as outlined here :lookhere: SLAMing Your Pool and brush the pool daily, especially the black algae. Pull out the light nich and clean behind it and replace it and soak your cart filter in a big bucket with warm water and powdered dishwasher soap for dishwashers.

Once you pass the Overnight FC Loss Test and you still have spots of Black Algae, run a slightly higher FC level and keep brushing the pool floor and walls where it is residing.
 
Continued. I filled the pool and I've brushed the pool by hand with the stainless steel brushes using scuba equipment. One can see plaster, dirt and algae much better up close. Plaster looks white from above.
I've been SLAMing and running filter 24/7. After hosing down the cart filter a couple of days, I soaked it in dishwasher soap. Pressure 8.5 psi.

Chemistry with TFP test kit:
CYA 40
TA 70
CH 500
pH 7.2
CC <1 ppm
FC. I've been reading FC before adding more bleach. I don't have readings at peak just after bleach. But before I add bleach, I run in the 10-14 ppm and add 3 qt to 1 gal bleach according to PoolMath target of 16 ppm for a CYA of 40. So far last two overnight FC loss tests show a FC loss of 2.5 and 3 ppm.

Though the water looks great and plaster looks white from above, the pool still has organics either dirt and/or black algae in the plaster up close with scuba mask.

Anything else to consider? I'll keep brushing and SLAMing.

Thank you.
 
+1, what she said. With your problem of having the algae etched into the plaster you really want to try as best you can to maintain 16ppm. If you need to target a little over like Abigail suggested I think it's a good idea to help you keep at 16 as much as possible.
 
DUH! I'll add more chlorine tonight and try to stay up longer to get a peak FC reading. Try to stay above 16 or so.

The light niche has metal and plaster and no algae. The light is on the coping and the niche is open to FC. Same with the niche for the closed main drain. No ladders, etc. Will look at skimmer again. Will try pics.

Thank you!

- - - Updated - - -

The "algae etched into the plaster" makes me realize that to remove black algae, one is removing micro-layers of plaster - right?

Latest chemistry:
TA 60 (was 70)
CYA 40 (steady)
CH 500 (steady)
pH 7.5 (rises gradually so add HCl periodically)
CC <.5
FC 9 ppm, added one gallon, after 45 minutes, got 15 ppm. Will add 3 qt to aim for 20 ppm FC by PoolMath. Added 1 gal to make sure.
 
"FC 9 ppm, added one gallon, after 45 minutes, got 15 ppm. Will add 3 qt to aim for 20 ppm FC by PoolMath. Added 1 gal to make sure."

Just so you know, if you go crazy with the bleach and damage something I'm tossing Abigail under the bus for telling you to go high and deleting my "+1" !!

Just kick me ... even when I wrote that I wasn't liking the word etch. Lets try clinging. Plaster has a course surface even if it feels smooth to the touch. Another member had such bad staining they actually put chlorine pucks on the surface for a day and it did clean some but there was still a stain. Don't know if you have a stain that isn't going to come off easily or it's live algae. They also tried going well over 30ppm and that didn't do it either.
For right now I'd focus on the SLAM and once you pass the three steps address the stains as they can't be live algae if you passed the SLAM.
 

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No worries.

At 11:45 pm I had a 15 ppm reading. I added one gallon of 10% bleach and got FC of 21 ppm at 1:00 am. CC is 0.5.

I will permanently close the pool if I have to do mustard levels! I drained the pool to get the CYA down so it would be overall less chlorine to treat the black algae. I'm adding half the amount of bleach from the higher CYA levels. But the new water will be expensive! Austin is a very environmental city. I feel guilty using water and I feel guilty adding tons of chemicals. Having a pool isn't good for the environment, is it? I do know I feel bad about the pool killing Hill Country Chipping Frogs and the occasional toad.

About the plaster. I haven't had a chance to research further. From above the water, the plaster looks great, smooth and white except for a few places where the old passive puck chlorine treatment chemically eroded the plaster. As the puck dissolves, it will chemically pit the plaster in a comet shape down the slope of the pool. More pitting is around the main drain where puck chlorine concentration settled more. So, pucks can chemically pit plaster and if it is used as a scrubbing device, damage plaster physically. There is not staining like metal staining.

About "micro-divots." I don't have an underwater camera to show you guys. Anyway, under the water with scuba equipment and mask, the plaster is not all smooth as you said. My plaster is coarse and not all white. It is generally alabaster like a skin but has tons of imperfections and divots (1 ish mm or less) with dirt and black algae. These divots seem to have dirt and/or black algae but there are other small specs that look like particles of "sand" that make up the plaster. I do not know if these divots are where the FC demand is. Where else?

Cleaning "micro-divots." I tried different things to clean these micro-divots out but one needs a toothbrush size tool where the brush is stiff like the stainless steel. A regular tooth brush was small enough but not stiff enough. A grout cleaning brush seemed to do the trick but the bristles were too coarse. If any brush is too stiff, like the 4 inch stainless pool brush, you can almost see the plaster (whitish clouds) coming off as you scrub.

I haven't researched what plaster is supposed to look like brand new. I have not been able to find any micrographs of black algae and how its colonies cling to plaster.

For biology sake, I can not find a discussion of the genus or species of blue green algae that might typically make up pool infections. My old college phycology text (Bold and Wynne) talks about the ability of some of the many blue greens to attach to rock or stone as a colony in water conditions.

Ultimately, though FC is used to treat human pathogens in pool water, it and water balancing is also used to protect the integrity of pools. Balance protects the pool from consequences of organisms and bad chemistry unhealthy to expensive pool structure and components. True?

SLAMing away!
 
I think if it were my pool, I would stop everything, take a deep breath, and decide what I wanted to do with this pool. I sense a lot of ambiguity and it is very difficult to instigate an aggressive plan (one way or the other) until you make a firm decision.

Based on what I hear, (not what I can see....got a pic?) I think that pool may need to be re plastered and may well be more than you are willing to spend.
 
Thank you. Yes, I am having trouble with a big body of water that I only enjoy the 3 most miserable hot months out of the year. But I am committed to keeping the pool balanced and sanitary until or if I do something different.

Here are some pictures:
Overall pool:
IMG_0450[2]_0001.jpg
Main drain and light niches:
IMG_0451[1]_0001.jpg
Close-up of puck comets with a little dirt still in them:
IMG_0452[1]_0001.jpg

Do I need new plaster?

Am I on the way to getting rid of the black algae?

Thanks
 
If you can get a some of this black stuff under your fingernail and smear it on paper and confirm black algae, you can get rid of it with a lot of elbow grease by brushing at the very least, daily and run a slightly higher FC level that coincides with your CYA level. Black algae likes to grab ahold of the nooks and crannies of plaster and pebbled pool finishes. It dies a slow death.
 
Thank you. OK, I will try to sample the micro spots. The pool looks much better - it used to look like a Dalmation a week ago. Still failing overnight FC test -third time. Dropped 5 ppm in 7 hours at night. Keep brushing, vacuuming, cleaning filter, SLAMing, etc. Have been aiming for 20 on the FC with 40 CYA.
 
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