Black Algae Confirmation and Questions

pirateyoshi

Silver Supporter
Sep 14, 2020
31
Orlando, Florida
Good evening TFP,

I just got my first house last month and it came with a ~7200-7500 gallon inground pool. It was pretty green when I first got it and I worked on it here and there until we moved in a few weeks ago. I have been shocking and brushing what I assume to be black algae for a while now, but not SLAMing with any actual accuracy since I just got my FAS DPD test today in the mail. I attached some pictures of the worst spots still- they are all on the deep side of the pool especially near the one step we have there. Since I can finally see the main drain now I do also notice some staining. I will put a picture of that out of curiosity at the risk of going off-topic.

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The pool had black algae around all the edges of the walls and it was much worse before these pictures. Kind of curious on how long to expect before realizing I am messing up or something else is afoot. I was a bit curious about if I should be draining throughout the SLAM process as well. My CYA is unfortunately around 70 but I don't have much in the way of draining besides the bib that's attached to my cartridge filter so its a very slow process and one I want to be careful about. Not sure if I am really supposed to be draining from there.
 

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ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
19,464
Northern NJ
Follow the SLAM Process and check your FC often and raise it back up to 28. Brush often.

No reason to be draining anything.

If the algae on the walls is clearing then the SLAM Process is working.

Nothing in your PoolMath logs to see what your chemistry is. What is your CC? How often are you checking the FC and how much do you lose over what time?
 

pirateyoshi

Silver Supporter
Sep 14, 2020
31
Orlando, Florida
I just downloaded pool math last night since I just got my FAS-DPD test. My process before was very much random but I knew at the worst I was limiting the growth of more algae and definitely not putting more than the SLAM FC.

I used liquid chlorine last night to try and bring it up to 28. My FC was 5.5 and CC 0.5 when I measured. I should have measured before I went to bed though because when I woke up today and measured my FC was only at 10.5. My CC was somewhere between 0 and 0.5 since it was much clearer but still a tiny tinge of pink when I added the reagent. I don't think I lost that much FC naturally and suspect the chlorine I got from Leslies 2 days ago was bunk. The lady there was very adamant to say their current batch sucked so I will use shock tonight to raise my FC since I need some calcium anyway. Will switch to bleach moving forward since I am done with that particular store...

I know the days I got the best progress were when I chalked the black algae spots with tablets but my CYA is way too high atm so I need to get Cal-Hypo tablets before I do that some more I think?

On a side note I bought a couple of bags of Calcium Hardness this last weekend and one of them was like really coarse sand (in color and feel). Didn't even think twice until I opened the next bag and saw the familiar white crystals. I have been vacuuming it away since it doesn't dissolve in the pool. Did water get into that package or something? Was very annoying to witness.
 
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pirateyoshi

Silver Supporter
Sep 14, 2020
31
Orlando, Florida
Well geez scratch any number crunching here as far as how much to add etc. My SO ran the volume calculations at first and chopped off much more than expected. My pool just went up from 7200 gallons to 12000 gallons after I ran the numbers myself... I still think the chlorine I bought from Leslies wasnt 10.5% but thats not as significant lol.
 

pirateyoshi

Silver Supporter
Sep 14, 2020
31
Orlando, Florida
Ok so with my new pool volume I measured the FC at 10.5 last night before shocking. Got it up to 28 and 0 CC and actually tested it this time before bed. I woke up at 8:30 luckily we have full cloud coverage and tested again and it was at 15.5 with some CC but less than 0.5. Scrubbed again and read some other posts about FC loss and decided I would take out my pool light... oh boy. Attached some pictures here and the metal compartment pictures was after I wiped all the baby puke and green algae from it. I don't know what the inside of this is supposed to look like so I guess I will make a separate thread for that.
 

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pirateyoshi

Silver Supporter
Sep 14, 2020
31
Orlando, Florida
Made a separate post for that and yeah really upset they couldnt have been bothered to keep the seal on the light. Now that I know its broken I don't have a choice but to fix it.

I did have a question about PH levels. Mine was at 7.4 going into SLAMing and I know I cant test for it during SLAM but it will generally go up over the SLAM process right? We have been having lots of rain so I was curious about how that all factors in.

My water looks so wonderful I wish I only had a normal algae problem because it would be time to jump in otherwise! Until then I keep scrubbing away. Maybe I will get a pumice stone because some of these spots seem very unfazed by my stainless steel brush
 

pirateyoshi

Silver Supporter
Sep 14, 2020
31
Orlando, Florida
I was looking over the pool today and noticed the only spots that have what I think are black algae are where the plaster is recessed. This makes sense to me because it gives it a place to root into. I never did check for false alarms though- I tried scraping off spots this morning was mostly unsuccessful. The two pieces I did manage to get off (and it was basically easier to scrape off plaster than it was these marks mind you) just feel like black little pebbles. They dont smear or anything. One of the pieces I was able to get off came with a little bit of plaster on it. The places I have the worst marks are all next to the steps or the very tops of the walls. Before I understood how big my pool was and was mock SLAMing, I ran though at least a dozen pucks scraping the plaster and things only flaked off when I went at it like I wanted to dig into something.

When I first got this pool it had tons of green algae as well and it naturally congregated in those areas a bit more, so I assumed it was black algae after being able to scrape some off with a puck back when. How do I really know whats black algae and whats ' small dark aggregate particles embedded within the plaster' that the Black Algae article on the site talks about? I have been enjoying the exercise but I hope I just haven't been eating away at my plaster for fun.
 

Rancho Cost-a-Lotta

Silver Supporter
Apr 10, 2018
1,562
Rancho Cucamonga, CA
I've only seen black algae once, on my parents pool. Their plaster is over 50 years old. Black algae was growing only in the pitted areas. I was able to scrape some of it off with my fingernail. When I wiped it on a piece of paper, it was distinctively green.
 

pirateyoshi

Silver Supporter
Sep 14, 2020
31
Orlando, Florida
I got another part off even though more plaster came off than anything and again just a hard piece of dark something. no stain or anything it feels very inorganic. I put vitamin C on it with no effect. Its very possible I have these 'anti-slip particles' in my pool and some Black Algae because my walls do look nicer in the month or so I have been trying to deal with the issue but since 100% of it is on pits in plaster as opposed to the first layer I just don't know what to think. Would it be crazy to take a bigger chunk out of the wall to see? Clearly need to touch up some of this plaster anyway...