Black Algae - when to drop FC level

[rlsnights]

Back again for more advice.

I have been running the pump on our 15,000 gal white plaster pool continously for about 8 days. I raised the FC to 35-40 ppm a week ago. Stopped losing more than 1-2 ppm FC overnight 5 days ago. Only losing 3-4 ppm during the day. We are brushing with SS brush at least once daily, twice on weekends.

We have seen NO CHANGE in the pool. Water is crystal clear but the black algae spots look just the same as they did a week ago. I expected to see some kind of change in at least some of the spots by now.

I'm nervous about dropping the FC level too soon but also nervous about damaging the plaster of our pool. Should I go ahead and start dropping the FC level now? How low should I drop it?

Should I adjust pH and TA after I've dropped the FC level? Does it matter which I do first if I need to adjust them?

Patricia
15,000 IG White Plaster Jet Vac sweep, cart filter, new pumps

FC 38
CC 0.5
pH ??
TA 110
CH 280
CYA 50

 

[frustratedpoolmom]

PH should be tested when your FC is below 10, otherwise it can read a "false-high" when the FC is above 10. Your TA is fine where it is for now, it can always be lowered later IF you are experiencing PH rise.

Sometimes the BA spots can leave behind stains. Are you brushing with a stainless steel brush every day?

To know if you are done shocking, your FC needs to hold overnight. So you test after dark, and then test again in the morning before the pool is exposed to full sun, and then compare the results. If you lose less than 1ppm of FC, you can stop shocking.

I would however recommend that you keep your FC at about 8 for awhile, running with higher than normal FC levels can help fade the stains/ensure the algae doesn't return. Sometimes the heads of the black algae are knocked off, but you have to keep brushing so they don't grow back, if the roots are still alive, inside the plaster.

Either way, I don't think you need to shock higher than 30 FC even with Black Algae.

 

[rlsnights]

Re: Black Algae - when to drop FC level/how to drop FC?

I feel like an idiot asking this question, but what's the best way for me to drop the FC level down to 8 from 30+?

If I wait for the pool to lose this much FC it will take a long time as we're only losing about 3 ppm per day.

Does it matter how fast I drop the FC?

Do you have a recommendation on how many hours a day and what schedule we should run our filter and sweep?

And yes, we have been brushing the pool at least once a day with a SS brush equipped with a wall whale to help make sure we had good pressure on the brush.

Thanks,

Patricia

FC 38
CC 0.5
pH ??
TA 110
CH 280
CYA 50

 

[JasonLion]

It is usually best to simply allow the FC level to come down on it's own. If you are in a hurry for some reason there is a chemical that will lower it right away, but that is not usually worth the effort/expense.

By the way, if your FC level is falling by less than 10% per day, you either have very little direct sunlight reaching the pool or your CYA level is significantly higher than 50.

The ideal pump run times vary from pool to pool and are usually best discovered experimentally. Note how the water looks, shorten the pump run time, give it several days to a week at the new run time, and see if the water still looks just as good. If the water is still looking good, try a shorter run time.

 

[rlsnights]

Thanks Jason,

At this time of year we are not getting a lot of direct sunlight on the pool. We live in Sacramento, CA - the city's nickname is City of Trees. Previous owners of the house thought it was a good idea to plant lots of trees in the back yard :? (but none in the front which faces south!). Between that and our neighbors trees we get shade on at least half of the pool even at mid-day at this time of year. Even in June at least 1/4 of our pool is shaded except at high noon.

I have tested the CYA level 3 times in the past week to make SURE that it was at the level suggested. Also, since we emptied half the pool and refilled it, we have done nothing to add more CYA to the pool. We have only added liquid chlorine.

Patricia