The Algae that would not die! Our 4th Battle Commences!

[Burdick25]

We have been battling algae all summer and have not been able to swim the entire year. We are currently experiencing our fourth occurrence of algae. We have an above ground 28 foot diameter round pool. Our filter is a sand filter. Our first occurrence was shortly after we opened our pool. Our solar cover was on and after a few days we noticed the algae. We used algaecide, 5 pounds of dry chlorine two days in a row, phosphate remover, metal remover, and floc. Then we vacuumed to waste. The water cleared up. Shortly thereafter, the algae came back. We caught it earler these next 3 times. We used enough chlorine to register well above 10 during these battles. We used floc to drop the algae and then vacuumed to waste (using a siphon). We changed the sand to Zeosand and dumped powdered chlorine directly into the filter to kill any algae there. We scrubbed the vacuum hoses with bleach water. We removed the stairs. We need help. Could the oak trees in our back yard be responsible? Could our well water, which is highly alkaline, be responsible? Our alkalinity is constantly 190 or above and appears to always increase. We dump in gallons of acid. At its lowest, the alkalinity was 150. Then our Ph goes down and when we put in Ph increase, the alkalinity goes back up followed by the Ph. Our water also has a lot of iron. We have an AquaChek meter. We have been unable to get both Ph and total alkalinity within the normal range. Yesterday our Chlorine was 7.1, Ph was 7.4, and total Alkalinity was 274. I added 1 gallon of acid and today the readings were 6.8, 7.0, and 250. I put in 2 more gallons of acid and 5 pounds of chlorine. Who knows what the readings will be tomorrow.

[Guest]

Hi.

When you use MA to bring TA down, you should aerate the pool to bring the pH back up.

It's really simple but can take a few weeks.

You can aerate by turning your eyeball up to break the surface of the water to create bubbles. You want to add alot lot of air bubbles... I use an air compressor.

Once your pH rises to 7.6-7.8, add more MA to bring the TA down and repeat the process by aerating *adding more air bubbles* to raise the pH back up.

See why I said it was a process?...

[chem geek]

As for the recurring algae, if you don't maintain at least a minimum Free Chlorine (FC) level that is 7.5% or more of the Cyanuric Acid (CYA) level, then your pool is at risk of getting green algae (for yellow/mustard algae prevention, even higher chlorine levels are needed). Do you know the CYA level in your pool and what your typical FC level was before the algae came back?

When you say "pounds of chlorine" that sounds like it could be Dichlor powder or Trichlor granular or Cal-Hypo granular. For every 10 ppm Free Chlorine (FC) added by Dichlor, it also increases Cyanuric Acid (CYA) by 9 ppm. For every 10 ppm FC added by Trichlor, it also increases CYA by 6 ppm. For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by 7 ppm. 6% unscented bleach or 10%/12.5% chlorinating liquid (or expensive lithium hypochlorite powder) will not increase either CYA nor CH.

The procedure for lowering the TA is shown here and is as described in the previous post: aeration at low pH with acid addition to keep the pH low.