Acid turning my pool Turquoise?

[hawley.35]

This is my first full summer with a pool (bought the house last year). I did a lot of reading decided I'd follow the TFP method this year and have only used liquid chlorine. We have a well and fill the pool with it. The water is hard, and has contains Ferrous Iron, so this year I've been adding softened water to limit the iron and calcium, and have been using Muriatic Acid and aeration to lower the Total Alkalinity (180-200ppm all summer). I thought I've been having algae problem, but I'm starting to second guess my diagnosis.

I completed a SLAM over two weeks ago. I waited for two consecutive days of 0 ppm CC, <.5 ppm overnight chlorine loss, and the water was crystal clear. I could see the detail of the liner in the deep end from 30 ft away. The PH and TA were high (7.8-8.0). I been adding Chlorine when it gets down to around 4-5ppm so the level bounces between 4 and 8. The water remained crystal clear.

Three days ago I decided it was time to lower the PH and added a gallon of MA. The pool turned vivid turquoise, and slightly cloudy, with a yellow dust on the bottom (pics attached). This is the pattern I've been fighting all summer. If I SLAM again it will go away in another two weeks, but will be my 4th SLAM of the summer, and the stores around here aren't restocking chlorine. It seems like the classic signs of algae, but I have been extremely cautious this time to not let my FC drop below 3ppm.

I thought this might be the Iron coming out of solution, but the Pool School article seems to say that it is High PH that causes that. What am I missing?

Full FT-100 Results
FC 7
CC 0
PH 7.4
TA 180
CH 375
CYA 35

 

[JoyfulNoise]

so this year I've been adding softened water to limit the iron and calcium

Explain this further … exactly how are you softening water ? Did you install a softener system?

 

[hawley.35]

Explain this further … exactly how are you softening water ? Did you install a softener system?

When I need to add water I am using water from the whole house ion exchange water softener. There is no softening or conditioning system on the pool, just a sand filter. The other option would be the hose tap that bypasses the softener and is untreated well water.

 

[hawley.35]

I should also say, I have not added water since before my last SLAM. With the dry weather and cool nights, I may need to soon, unless I just close the pool for the season.

 

[hawley.35]

Well...I guess it was algae. A few days later it was dark green. I'm in the middle of another slam. Now I just want to know why adding acid seems to be causing algae blooms. Does a PH between 7-8 have that big of an impact on Free Chlorine?

 

[Mdragger88]

Are you keeping poolmath logs? If so can you share them in the settings ?


The acid and the algae bloom are unrelated.
Not sure what to make of the immediate color reaction.
Have you added any other chemicals/pool potions to the water recently?

 

[hawley.35]

Unfortunately I don't have logs. I can say that everything but the Free Chlorine was incredibly stable all summer. The pool was taking about a gallon of 12.5% bleach a day (4ppm) until after my last slam, after that it was closer to half a gallon.
Is there something you're looking for?

As far as chemicals the only things I've added are Chlorine, Muriatic Acid, and one dose of classifier early this summer to try and speed the the clarifying during a slam.

 

[Mdragger88]

Bromine being in the water can have a similar color changing effect after the addition of acid but it sounds like that’s not the case here.
Sodium bromide is found in some yellow out algae products and people unknowingly turn their pool into a bromine pool with them.

 

[hawley.35]

Is there a maximum bromide level for a chlorine pool? I don't think I can test for it, but I assume a pool store could in a one-off. I've only owned this house and pool for a year. I've got no clue what the previous owner put in it.

 

[Mdragger88]

If it were a bromine pool the fc level you’re measuring wouldn’t hold long at all as bromine is not protected from the sun by cya & is quickly depleted. (Which is why we don’t recommend using bromine in an outdoor pool. )
The fc test & the br test are the same - you just multiply the fc results by 2.25 there is no way to differentiate between bromine & chlorine with the oto, fas, fas/dpd or strips.
If you haven’t experienced that behavior in all this time nor have used any bromide containing products then you’re measuring fc & bromine/bromide is not the issue here.

 

[Mdragger88]

How’s the slam going?

 

[hawley.35]

Crystal clear, 0 cc...just in time to close.


Maybe I'm just misunderstanding what's happening in the pool when I slam. If you look at the pics in my first post there is a yellow "dust" on the bottom of the pool. It is so fine is almost impossible to vacuum without stirting it up. I'm not sure if that is algae or iron. After a week or so it disappears overnight, and the water goes from green/cloudy to a power-blue and cloudy. I always assumed this was the dead algae, but there did it go? It's usually another 7-10 days until the water is crystal clear. All the hurricane rain slowed it down this time.

 

[Mdragger88]

The dead algae gets trapped in your filter. The slam is killing it so it stops proliferating faster than your filter can remove it.
Have you passed an Overnight Chlorine Loss Test?

 

[hawley.35]

Zero loss last night.

It just amazes me that the bottom can look like this (pic attached). Then be almost clean overnight. Even without vacuuming. Then it takes the filter another 10 days to clear the cloudyness out of the water.

Sometimes I can't even vacuum the whole pool before it is to stired up and cloudy to see what I'm doing. I even tried 1micron diesel filters on the returns (second pic) and it went right through. I guess that's why I was doubting the algae diagnosis and getting wrapped up in thinking it was iron.

 

[JamesW]

Looks like mustard algae.

 

[JoyfulNoise]

Sand filters suck at clearing pools. Just saying …. they do suck. Well, the pump sucks, but the filter does a lousy job with fines.

 

[dereksanders]

Added DE helps quite a bit.

 

[hawley.35]

Looks like mustard algae.

That's it, the search term I needed. No surprise that the top Google link is the the TFP Pool School article on Mustard Algae.

Looks like I have a new minimum and slam level. I think I'll be closing tomorrow. So I bumped the FC up over the mustard slam min this afternoon. I read some where here that below 60 degrees water temp alage slows, so let's hope I don't have a swamp next spring.

Thanks everyone.

 

[Mdragger88]

The Mustard algae protocols are to be implemented AFTER completion of the
SLAM Process (meeting all 3 end of slam criteria) at normal slam fc levels.
Whats the closing rush? Are you closing yourself or with a service?
What is your current water temp?