Black algae cya 60 ppm. FC 72 ppm?

#1
My pool has black algae and I read that I should go to 3x shock level and brush and run the pump till it's gone. Pool calculator says 6.6 gallons to reach 72 ppm. Should I use liquid bleach or powder shock? I don't want to raise cya over 60. All other levels are good. Thanks!
 

AimeeH

LifeTime Supporter
TFP Guide
Apr 2, 2012
1,997
Columbia SC
#2
Hi. Welcome to TFP :)

Where did you read 3x "shock" level is required to rid black algae? There is an article in pool school on black algae here : Pool School - Black Algae

Can you give us a little more information like pool size, surface, testing method and full results? You may have a problem that isn't black algae.
 
OP
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#3
Swim University has a video and the guy says to add 3 pounds of shock for a 10,000 gal pool. That's 3x shock level which is also how he describes the strategy. My pool is 10,000 gal marcite with a 8412 cartridge filter. I use DPD chlorine test method. The guys at pinch a penny said it was probably black algae since my pool is pretty old and will need re-marcite soon. I only check chlorine and ph at home. I let the folks at pinch a penny check the other values since I am in there every week. I added 4 lbs of stabilizer a week ago and now it's reading 60. I only use pench a penny liquid chlorine, no tablets. I try to keep my fc between 6 and 8. I add acid or baking soda and calcium etc when they tell me to. Pool looks great right now except for the terrible black spots (lots of them). Temp is 71 deg F though. Too cold for me but I love having my morning bfast and coffee by the pool in the morning and just lounging by it whenever I can.) Mahalo!
 

Dz7

In The Industry
Jun 20, 2016
32
Florida
#4
Swim University has a video and the guy says to add 3 pounds of shock for a 10,000 gal pool. That's 3x shock level which is also how he describes the strategy. My pool is 10,000 gal marcite with a 8412 cartridge filter. I use DPD chlorine test method. The guys at pinch a penny said it was probably black algae since my pool is pretty old and will need re-marcite soon. I only check chlorine and ph at home. I let the folks at pinch a penny check the other values since I am in there every week. I added 4 lbs of stabilizer a week ago and now it's reading 60. I only use pench a penny liquid chlorine, no tablets. I try to keep my fc between 6 and 8. I add acid or baking soda and calcium etc when they tell me to. Pool looks great right now except for the terrible black spots (lots of them). Temp is 71 deg F though. Too cold for me but I love having my morning bfast and coffee by the pool in the morning and just lounging by it whenever I can.) Mahalo!
Is the black algae only on the bottom? Or is it on the sides as well? Did you get a stainless steel brush or are you using a regular nylon or polyester brush?
 

domct203

Bronze Supporter
LifeTime Supporter
TFP Guide
Jun 3, 2015
3,959
CT
#5
Welcome to the forum!

I would advise against any more 'swim university' videos. Raising your FC to 120% of your CYA was not only a unnecessary waste of FC & money, it will be vary harsh on all the pool equipment.

If you do have black algae, it needs to be physically removed from the surface to expose it all to chlorine. Black algae will grow roots into the pool surface, as well as a tough biofilm 'skin' to protect it from the chlorine. A good stainless steel pool brush and a bit of elbow grease will go a long way here.

Please read through the Pool School article on black algae that AimeeH posted. It is a tried and proven process that will eliminate the black algae from the pool's surfaces.

Don't hesitate to ask any questions you may have.
 
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#6
Steel brush, check. Elbow grease, check. Since it's too cold to swim I will keep the chlorine on the high side and keep brushing. The black spots are on the bottom and in corners and on horizontal surfaces where the plaster is pitted. Smooth vertical areas look good for now. I will keep you posted. Thanks.
 
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#7
Update. I took a chlorine tablet that was left over from last year in put it on top of a solid spot of the same size. I had been brushing the spot vigorously with the wire brush but wasn't seeing any progress. After sitting on the spot for 4 hours I moved the tablet and the dark color was gone. I can still see the faded area but no black. I am now tempted to do the same with the dozens of other spots. I will continue to brush and maintain high FC hoping to remove all traces and get back to white plaster.
 

Patrick_B

TFP Expert
LifeTime Supporter
Jun 7, 2011
14,999
Midland TX
#8
Welcome to TFP!

We can help you get this under your own control and eliminate any guess work If you like Harrell. Mixing our advice and theirs will only add frustration to your pool care routine. Let us know if you'd like to try.
 
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#9
Thanks Patrick! I definitely want to learn the most efficient and cost effective way to care for my pool. I've been moving that tablet from spot to spot and it is working pretty well. Do you think I might be creating any unforeseen circumstances by doing this?