Black Algae cleanup

[cactus_LV]

Hi,

6 weeks ago our pool started growing black algae (now I know that it’s black algae). At that time I didn’t have time to take care of it so I let it grow for 2 or 3 weeks - initially I thought it was just some discoloration from leaves on the ground. Shouldn’t have done that … I know.
Anyway based on other threads on here I did the following:
- SLAMed the pool for the last 7 days
- brushed it every day twice - initially with the nylon brush but that didn’t do much now with a wire brush
- added algicide (not recommended here but I was concerned that the algae will continue to live in the pipes or other places which I can’t see or brush)
- brushed granular chlorine on the floor (since ‘normal’ slamming didn’t help) that finally helped

Now it looks much better. Still some patches but not super obvious.
I want to replace the water now to get ride of the algicide and was wondering if once the pool is empty I should use that time to pressure wash, chlorine wash or acid wash the pool just to make sure that everything is gone. If not should the smaller lighter patches disappear just by brushing and keeping the chlorine high?

FC 10-15 ppm
PH 7 - 7.2
TA 80
CH 450
CYA 30 (I know little low for SWG - not sure where I did my math wrong)

And I assume this all started most likely because our acid pump stopped working and I didn’t properly manage the PH manually.
Any input is appreciated.

 

[PoolStored]

Hold the line for @Katodude our BA expert...

 

[Katodude]

Unless it was copper based algaecide no need to drain. If it was copper based, I will let another expert give you that advice.

Otherwise BA requires disrupting the surface of the algae. Wire brush works. I personally like a weak pressure washer. Then bathe the algae in high does LC. Either pour the strongest LC you can find over the area and let it wash over the area you just cleaned. Or get a 1 gallon pump sprayer and get in the pool and spray those sections.

After you cleaned everything you need to maintain FC at about 20% of your CYA for a few weeks.

And now the bad news, you will have to run FC hot for the rest of the time that pool exists (about 15% of CYA) to keep it from coming back.

Welcome to @Newdude club #runshot

 

[cactus_LV]

@katodude thank you so much for the quick response!
Unfortunately the algaecide was copper based.
Once I drained the pool can I use a weak pressure washer to clean the affected areas (and use LC instead of soap in the pressure washer)?

Running FC hot just means more than the minimum at 15% (30 CYA) I will need to keep it at least at 4.5ppm forever?

 

[Katodude]

Just be super careful in an empty pool with the pressure washer. You dont want to damage your plaster. I don’t know how a pressure washer will react to having LC running in it?

If the pool is empty mix a diluted LC mixture in a pump sprayer and spray those spots. I would also rinse it off pretty quickly, you dont want to bleach out your plaster.

You are in Las Vegas I would run your CYA a little higher than 30, probably closer to 50. Then keep for FC at 7.5 pretty much forever. I try to keep my FC around 12.

 

[cactus_LV]

You are in Las Vegas I would run your CYA a little higher than 30, probably closer to 50. Then keep for FC at 7.5 pretty much forever. I try to keep my FC around 12.

Don’t you smell like chlorine every time you go in the pool with that much FC?

 

[mknauss]

If you smell chlorine, those are chloramines, or CC, and you likely need higher FC levels.

 

[cactus_LV]

Ok that makes sense given the algae. I thought high FC also makes your cloth smell like chlorine.

 

[Katodude]

It the ratio of FC to CYA that is important. My FC at 12 with a CYA either at 70 or 80 is less harsh than FC at 3 with CYA at 0.

And no my pool does not smell, and nothing gets faded in the pool.

 

[Parac]

(and use LC instead of soap in the pressure washer)?

No, you don't want to put chlorine in the pressure washer soap dispenser. It will wreck the seals. There are chlorine injectors your can get, but you are probably better off doing the pressure washing and chlorine separately.

 

[cactus_LV]

Thank you everyone for your help. Pool is refilled and chlorine wash done. All BA is gone and hopefully it stays that way. I decided not to use a pressure washer and go with a watering can instead to run the chlorine water solution down along the walls (and scrub like crazy). It still dried up very quickly. I think a sprayer wouldn’t have worked in our dry climate.

 

[cactus_LV]

My FC at 12 with a CYA either at 70 or 80

I am curious why your CYA is so high?

 

[PoolStored]

I am curious why your CYA is so high?

@Katodude can speak for himself, but being in Palm Beach, a high CYA reduces FC demand. Lower FC demand means less use of the SWCG. Less use of the SWCG means longer cell life.

I do the same, even here in Ohio. My CYA is 90, I keep FC at 10-12. My RJ-60 SWCG loafs along at 5-10% output, 24/7. With a lower CYA around 60, I need to keep it closer to 20-25%.

 

[Katodude]

^^^^^ What he said.

 

[cactus_LV]

But doesn’t a high CYA also mean that the chorine is less effective? Less is lost to the sun but since it’s protected by/ bound to CYA it’s also not able to sanitize as much?

 

[PoolStored]

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This thread presents my findings so far on pool water chemistry including the following: More Accurate Calcite Saturation Index (CSI) to replace Langelier Saturation Index (LSI) Calculation of ppm HOCl (disinfecting chlorine) at various levels of Total Free Chlorine (FC) and Cyanuric Acid (CYA)...

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