Black Algae and High Phosphates

TB1111

Member
Dec 3, 2024
8
Tampa Bay
Hi All,

New to forum and looking for some guidance. I recently purchased a home in Florida with a pool and jacuzzi. The local Pinch a Penny has been servicing the pool and due to the back to back hurricanes in October and moving haven't really had a chance to pay much attention to pool. That said, I notice some small black spots on the bottom of the pool which i thought were droppings from the palm trees and perhaps the pool company wasn't vacumming. I took a video and sent to the pool company to which they said that's black algae. My first reaction was why the heck are you not informing me that there is black algae and continuing to generally service the pool as if everyhing was normal (no good response here). So I terminated the service and am now trying to work this via pool school OTJ. That said, I noticed the DE Filter pressure was running at 30 PSI and found that this was off the charts and filter probably clogged. I then proceeded to clean the DE cartridge (video attached) and it looks like it hadn't been done in a long time. I asked the Pinch a Penny why this was overlooked and they said the previous owner never requested to have the DE filter broken down and cleaned which is an extra service. I can't for the life of me figure out how they can service a pool and see the equipment under duress and the filter over pressurized and black algae and continue to service.

WIth all that said, I am trying to figure out how to get the black spots off as I have tried scrubbing with a chlorine tablet on the end of pole with that puck extension contraption but they aren't budging. Tested my water today and although its clear as day and the filter is now clean there is no chlorine and the phosphates are off the charts. They told me to put a full bottle of suncoast phosphate remover, backwash and then retest berfore adding chlorine which I was about to do until I saw warnings against that. I was thinking about just draining the pool halfway, trying to remove the spots and then refilling with more new water. Any guidance would be appreciated!

  1. Pool Spots Video Pool Spots.mov
  2. Dirty DE Filter Video: Dirty DE FIlter.MP4
  3. 30 PSI Pump Video: 30 PSI .MP4

Thank you!
 
Welcome to TFP.

What does phosphates off the charts mean? Numbers, please?

What test kit are you using?

@Katodude is our black algae whisperer and advises picking at the black algae spots with some sort of physical method: wooden stick, wire brush, or, my personal favorite, weak pressure washer. Then, apply the strongest LC to those spots: pump sprayer, dump jug over the spot—more than once is better. Then run FC hot.

You have to disrupt the black algae. If you have less than ten spots, use a bamboo BBQ skewer. If you have more, a weak pressure wash will make quick work of it. Get in the pool with a mask and snorkel and have at it. Some do not like the wire brush method and think it is too aggressive.

Then, apply the strongest Liquid Chlorine to those spots as you can. Either dump it and let it flow over or get a pump sprayer. Some have gotten lazier over the years and just dump. Sure, it uses more chlorine, but you probably need to raise your level anyway.

Run FC at 20% of CYA for at least several weeks.

This is the part that sucks; run FC for the rest of the time at a minimum of 12% of CYA; 15% is better.



 
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Ok thanks.. Off the charts was it was the max that Pinch a Penny can test for on the paper TDL's 4500 ppm (not sure if that's Phosphates but the printout doesn't indiciate that specifically. There's probably 20 to 25 spots all less than the size of a penny. I do have a pressure washer and pump sprayer so I guess I can use like a 25 psi nozzle or something less? Will try and figure out how to run the FC and CYA etc after I blast the spots and dump chlorine on them.
 
Ignore the phosphates. At least for now. If you want to mess with them after your pool is clear go ahead. There is plenty of good advice about phosphates on this forum and what to actually use. In any case phosphates did not cause your problem.

Allen pretty much summarized what I would tell you to do. You have to pop off those black algae spots. Pressure washer inside the pool is my favorite. Then figure out how to get as much concentrated chlorine on those spots as possible. Do it a few times. The last bit of advice about running hot is important. You now have a pre existing condition. The moment your FC drops you will get black algae spots again.
 
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I just finished pressure washing (had a 10 foot extension wand with 25 psi adapter). Not sure how long I am supposed to spend over the spot or if that's too much or too little pressure for pebble tec. The algae did not budge but I spent some time whacking at it with the PW. I just poured LC over the spots using PVC pipe. Turned pump off so let's see what happens.
 
Ok thanks. What does running FC hot mean sorry I am poolilliterate?
You need to run the FC levels at 20% of CYA for several weeks after initial treatment and then at 15% of CYA level for the life of the plaster.
 
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Here is a thread about copper staining…


Does your spots look like the pictures?
 
Here are a couple of pictures.. The spots have not spread or changed in over a month and doesn't matter what I hit them with they don't seem to budge.. I am wondering if its something else altogether myself. We have a jandy salt chlorinator and DE Filter. I also just used Pinch a Penny Black Algae suncoast black algae remover and had that sitting on spots 24 hours and still didn't seem to budge.
 

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  • Pools Spots 1.jpeg
    Pools Spots 1.jpeg
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  • Pool Spots 2.jpeg
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Take a bamboo skewer or a finger nail and scrape them, then wipe on a paper towel. Show us a picture of the paper towel...
 
Yep, same stuff as in chlorine pucks. If you sat trichlor on a spot for a day and it didn't lighten at all then it's possible you're looking at metal staining and not black algae.

Follow PoolStored's advice and see if you're able to scrape some off. If not, then I'd investigate the possibility of metal staining. Have you been using any kinds of algaecides or an ionizer of some sort?
 
Or powdered shocks / pucks that are '3 in 1' or such ? Those usually have copper in them and are frequently used by pool stores/services.
 
Ok.. I am pretty sure it's probably metal staining as nothing comes off on scraping. I am going to heat the pool up and get a mask on to confirm so I appreciate everyone's help here what a great resource!

Crush up some vitamin C tablets to create a paste in a sock and rub it on the spots. If they lift it is iron stains.


 
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