I need to help my boss with Black Algae!

[jnorris]

My boss has a gunite in-ground pool with spots of Black Algae appearing in the pool. She uses either Tri-Chlor or Di-Chlor tablets exclusively for chlorination. I tested her water for her (I have the good Taylor kit), and here were her numbers:

FC zero
CYA well over 100 (100 is the highest my test kit goes, and before I even got to the 100 mark, I could no longer see the black dot)
PH 7.4
TA 100
Calcium 400

I am not sure what they use to shock, but I'm wondering if it is Cal Hypo, due to the high Calcium level.

I need to give her instructions on how to rid her pool of black algae. I know what to do, but she needs to hear it from the "experts"!

 

[JasonLion]

You need to get the CYA level down, preferably to around 50.

Black algae is no fun at the best of times. The traditional approach is to shock the pool for several days and brush the black algae very frequently. A faster approach is to shock the pool and use a pressure washer to wash off the black algae while the pool is at shock level. Neither one will work well until you get the CYA level down. Unfortunately, lowering CYA requires replacing water.

 

[duraleigh]

Judy,

She should register here and learn for herself. Attempts to convince someone second-hand almost always result in failure and frustration.

 

[jnorris]

Judy,

She should register here and learn for herself. Attempts to convince someone second-hand almost always result in failure and frustration.

I agree Dave! I tried that first. Now I am looking for you guys to spell it out, so I can print out this thread and say "there's your answer". They think I'm crazy to pour "laundry bleach" into my pool!

 

[Guest]

tell her that laundry bleach and liquid chlorine are exactly the same chemical and this imformation comes from someone who both works in a pools store and does commercial pool maintenance!
ALSO teel her that the first step is to drain and refill until the CYA is between 30-60 ppm and then the way to kill the black algae is a LOT of liquid chlorine or bleach added several times a day, a wire algae brush to scrub the algae (the cell wall needs to be broken to kill it) several times a day, and a lot of patience. Black algae is an indicator of a severely neglected pool. It takes weeks to appear. It also takes weeks of work to get rid of it.

Once she gets it under control she needs to watch her CYA and possibly stop using trichlor (or use it responsibly!) to prevent future problems.

 

[jnorris]

UPDATE: My boss told me they bought "unstabilized" granular shock and used that to shock her pool, and rented a scuba tank and went in and scrubbed the black spots with a chlorine tablet.

They won't switch from using the chlorine tabs, so I guess she will handle things on her own now!