Algae & White Powder Issue

[fmp]

My pool has been producing lots of white powdery/sandy precipitate this summer, at least a few cups a week. I guess it is probably calcium phosphate? I also have been battling moderate black algae on the bottom of the pool but the water is clear.

Here are my numbers:

SWG
FC: 8
TC: 8
TA: 70
pH: 7.6
CH: 1300
Phosphates: 4ppm
CYA: 50
Salt: 3000
Temp: 85-90

So I am guessing that the combination of high temp and high CH and Phosphates plus the SWG and sources of aeration is causing this precipitate. I think the precipitate is helping the algae grow and survive. Is my best option a drain and fill? Tap water is CH: 250 & Phosphate: 0.8.

Thanks

 

[Texas Splash]

fmp, welcome to TFP. No doubt your CH is an issue worth monitoring closely, along with pH and TA. Couple things that may help us get you a better answer:
1 - Can you tell us what type pool you have (plaster, vinyl, etc); and a better idea of your location please?
2 - What test kit did you use for these readings?
3 - Have you tried entering all of your test results and pool info in the Poolmath calculator so that you could compare your CSI level?

Generally speaking, I would not think to relate the causes of algae to the powdery substance unless it is dead algae perhaps? Your reply might help us evaluate your scenario better.

 

[duraleigh]

Phosphates (where did you get that reading?) have no relationship to mineral precipitation. read "The ABC's of Pool Water Chemistry" up in Pool School. That'll give you a better understanding of what chemistry you need to learn.

How do you know it is black algae on the bottom of your pool? Please list your statistics so they appear at the bottom of your post so we can help you.

Please fill out city and state

 

[fmp]

Phosphate reading comes from LR phosphate test. Other readings are from taylor kit. Calcium phosphate is a possible precipitate, right? So how can it not be involved?

According to these calculations: What phosphate ppb will precipitate calcium phosphate?

critical phosphate concentration when pH drifts to 7.8 is 3.16ppm. Mine is at least 4.

Black algae because of the growth pattern and when brushed exposes the green inner layer.

Maybe the precipitate has nothing to do with the algae, but the fc level has been 5+ for months and the algae still hangs on. But there are at least anecdotal connections between phosphates and algae.

 

[Texas Splash]

fmp, based on your additional info, I would breakdown your situation into two possible scenarios:
1 - Algae: If that is indeed black algae, your initial treatment would still require a SLAM via Pool School - SLAM - Shock Level And Maintain. It's possible it has been allowed to thrive because your CYA level listed above (50) is below your recommended range (70-80). This forces your SWG to work harder, and leaves your FC more exposed to that AZ sun. There's not much room for error with a SWG pool, so if your FC ever dropped lower than 4, it would be easier for algae to grow and/or sustain itself. It is true that black algae can be a bit more stubborn, and different pool surfaces sometimes play a factor in it's resilience, but you should have no problem eradicating it. Typically the advice is to try and expose the surface of the black algae to allow the bleach to penetrate the algae. Carefully scraping and/or scrubbing the algae may be required for the SLAM to work effectively.
2 - Calcium Phosphate and Precipitate: This discussion could (and may) get much more deeper by others, but I'm going to try and keep it simple. Because your CH is high, I found that by lowering your TA to 60 and your pH to 7.4, it had a dramatic effect on changing your CSI and bringing it closer to zero on the scale. Perhaps that may help with the precipitates you are experiencing. We have some other Southwest members who live with extremely high CH who may reply wit their personal experiences of precipitates, but either way, managing your CSI will be a critical factor in confirming when the time is right to start with fresh water,
Best of luck to you, have a nice day.

 

[fmp]

fmp, based on your additional info, I would breakdown your situation into two possible scenarios:
1 - Algae: If that is indeed black algae, your initial treatment would still require a SLAM via Pool School - SLAM - Shock Level And Maintain. It's possible it has been allowed to thrive because your CYA level listed above (50) is below your recommended range (70-80). This forces your SWG to work harder, and leaves your FC more exposed to that AZ sun. There's not much room for error with a SWG pool, so if your FC ever dropped lower than 4, it would be easier for algae to grow and/or sustain itself. It is true that black algae can be a bit more stubborn, and different pool surfaces sometimes play a factor in it's resilience, but you should have no problem eradicating it. Typically the advice is to try and expose the surface of the black algae to allow the bleach to penetrate the algae. Carefully scraping and/or scrubbing the algae may be required for the SLAM to work effectively.
2 - Calcium Phosphate and Precipitate: This discussion could (and may) get much more deeper by others, but I'm going to try and keep it simple. Because your CH is high, I found that by lowering your TA to 60 and your pH to 7.4, it had a dramatic effect on changing your CSI and bringing it closer to zero on the scale. Perhaps that may help with the precipitates you are experiencing. We have some other Southwest members who live with extremely high CH who may reply wit their personal experiences of precipitates, but either way, managing your CSI will be a critical factor in confirming when the time is right to start with fresh water,
Best of luck to you, have a nice day.

Thanks for your response. The black algae is really a pain. I can only stand to do so much brushing. But as the weather cools off a little bit it will be more tolerable. I wish they made a robot with a steel algae scrubbing brush.

I will look at adding more acid to reduce those parameters. Falling temperatures should also help reduce the precipitation. Either way I think the pool is probably due for a water exchange. The SWG is requiring a cleaning once a month with the current levels. I will probably wait until winter water rates go into effect.