Black Algae....ugh

[ILpoolprobs]

Hey Everyone,

I know there are a lot of threads on this already...just looking to see what your thoughts are.
At the beginning of July, I had metal stains on the floor of my vinyl liner (liner is old....8-12 years).
Yes I plan to replace it.

So I used a chlorine neutralizer and citric/ascorbic acid to eat the stains away...which worked pretty good.
After which however, the pool balls I was using in my Hayward kept jacking up the pressure until backwashing was perpetual, causing stagnant water.

Everything seemed fine until we went on vacation and the pool was stagnant for a longer period... Black spots started showing up at the end of July.
I switched back to sand and within days the pool was crystal clear and I could see the scope of the black...it's bad.

Tried algaecide (yes I know, I am an idiot then I went back to scrubbing and shocking but am guessing I didn't stick with it long enough.

So here I am...back on the forum.

TF-100 test results
-FC 4
-CC .5
PH is high (see photo) - Tested while FC at 4 per TF-100
TA 140
CYA - 40-50
Pool Temp (89F) - Yes we are crazy
Salt ~3,000

I just added a 1.2lbs of chlorine granules hoping to both get my FC up to at least 8 and also hoping some will settle on the bottom to help eat the algae.
Just brushed and brushed the pool along with scrubbing with the only mitt I can find that actually helps get this black Crud off.
Backwashed and shut pool heater off.

The pictures were after I brushed thoroughly and scrubbed...so if you see streaks of white...that's me using the red mitt basically scraping it off (it's incredibly tough in the transition to deep end 4-8')

Questions....
According to the FC/CYA 8 is a good FC level to hold during SLAM....right? or should I go higher?
Should I address the PH or wait until after Loss Test is complete?
Is my 5yr old TF-100 test kit too old?
Any other ideas?

Thank you for any advice... as I start SLAM over this holiday wknd....tons of photos attached.

-Brand new SWG this season
~20,000gal inground, vinyl liner needs replacing as it is getting wrinkled
-Hayward s244T sand filter (now back to sand again)
-Jandy PHPF 1.5hp Pump

 

[ajw22]

Welcome to TFP.

Black algae rarely to never forms on a vinyl liner. It need the nooks of plaster to attach to. I doubt you have black algae.

5 years is too old for reagents. Order a refill set.

Follow the SLAM Process step by step without taking shortcuts, which you are doing.

SLAM FC for CYA 50 is 20. Use liquid chlorine during the SLAM Process.

Brush often during the SLAM Process

The black spots may be more metal staining.

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[ILpoolprobs]

Shoot you are correct....I went to the wrong tab and didn't click on the SLAM tab for the proper chart.
Quick update.

I tested at 9pm, FC=9, CC=.5
Just tested the pool again at 10:30am, same results. No change granted the SWG is running at 85%.

If it is metal stains....would the higher FC oxidize the metals making it worse?
Based upon the test results....should I quit SLAM and treat the metal stains?

I assumed it was black algae because along the crevaces of the built-in seats I can scrape off stringers.....and when I brush sometimes I get cloud of yellow/green.
However I am seeing more areas of reddish appearing making me think iron. Those areas are also rougher to the touch....

Continue SLAM or kill the chlorine, adjust the ph lower, and go with AA?

 

[ajw22]

You can not do the Overnight Chlorine Loss Test with your SWG running. If your SWG was running at 95% and your FC did not INCREASE then it is likely the algae consumed it.

Slow down and follow the process. Turn off your SWG tonight and do a proper Overnight Chlorine Loss Test.

You could have algae and metal staining.

Crush up some Vitamin C tablets and put it in a sock and rub it on some of the stains.

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[ILpoolprobs]

Grabbed some Vitamin C tablets and hopped in the pool. The large patches of reddish brown basically vaporized almost immediately, while the black spots were more stubborn.
Not sure if the black responded to its acid or if having a hard tablet to scrape with did it...but some little spots of black were removed.

Will SLAM at 20........then check OCLT in the morning....