Weird chemistry and yellow algae

[gulfbeach]

I am scrubbing my pool every other day to keep up with the algae on the walls.
Here’s my current chemistry: pH 7.8, FC 5, Alkalinity 70, Calcium 80, CYA 100, Temp 85 .
Prior to reading the blogs, I added Copper sulfate as well, probably 0.5 ppm if I did the math correctly.
I have only ever used tricolor pucks in an inline feeder, hence the high CYA.
The pool is 40,000 gallons with a fiber filter and a heater and variable speed pump.
The water was new 4 years ago and gets drained about 25% once a year.
Any suggestions on how to get this back in balance and conquer the algae?

 

[JohnT]

Welcome to TFP!

Because of the nonlinear scale of the test, it’s possible your
CYA is even higher than you measured. This causes problems when trying to control algae.

If you follow the FC/CYA Levels, you’ll see 5ppm is much too low to stay clear. You should be aiming for more than double that concentration.

I’d recommend you find out for sure what your copper level is. Copper and CYA can only be removed by replacing water, and you likely need to lower both levels.

 

[PoolStored]

With a CYA of 100, do the diluted CYA test, #8 here:

CYA - Cyanuric Acid Test

Cyanuric acid (CYA) is the chemical name for the product commonly called “pool water stabilizer” … Read more…

www.troublefreepool.com

Report the result.

You will likely need to replace some percent of your pool water to reduce CYA. CYA reduction is 1:1 so a 50% replacement will lower your CYA by 1/2.

Read "no drain water replacement" here:

Draining - Further Reading

www.troublefreepool.com

 

[pjt]

Here’s my current chemistry

How are you testing?

 

[Bperry]

I am scrubbing my pool every other day to keep up with the algae on the walls.
Here’s my current chemistry: pH 7.8, FC 5, Alkalinity 70, Calcium 80, CYA 100, Temp 85 .

Calcium hardness level of 80ppm is very low. What test gave you that number? Seems hard to believe unless you fill the pool with softened water.

 

[gulfbeach]

How are you testing?

Using a Taylor kit, maybe a 2600. All done by titration.

 

[gulfbeach]

Calcium hardness level of 80ppm is very low. What test gave you that number? Seems hard to believe unless you fill the pool with softened water.

I am in New England and our water is naturally low in everything but iron and radon. I will check again as I was thinking about adding calcium if that number is correct.

 

[gulfbeach]

With a CYA of 100, do the diluted CYA test, #8 here:

CYA - Cyanuric Acid Test

Cyanuric acid (CYA) is the chemical name for the product commonly called “pool water stabilizer” … Read more…

www.troublefreepool.com

Report the result.

You will likely need to replace some percent of your pool water to reduce CYA. CYA reduction is 1:1 so a 50% replacement will lower your CYA by 1/2.

Read "no drain water replacement" here:

Draining - Further Reading

www.troublefreepool.com

Thanks, I was afraid that was going to be the solution. My water bill is pretty high already.

 

[gulfbeach]

Welcome to TFP!

Because of the nonlinear scale of the test, it’s possible your
CYA is even higher than you measured. This causes problems when trying to control algae.

If you follow the FC/CYA Levels, you’ll see 5ppm is much too low to stay clear. You should be aiming for more than double that concentration.

I’d recommend you find out for sure what your copper level is. Copper and CYA can only be removed by replacing water, and you likely need to lower both levels.

Thanks, time to turn on the hose.