Can you do everything right and still get hit with algae?

[algonquinforestpool]

Hello! This is my third pool season and I finally feel like I know what I'm doing thanks so this site (yay!) and have enjoyed a beautiful, crystal clear pool all summer until... two days ago. We came back home from 6 days at the cottage to a mildly cloudy pool with what looks like dust sitting on the walls (I assume algae? I've never ever seen this before). My mom visited the pool every day to swim and ran our robot vacuum every day. The filter runs 12 hours a day and I had the SWG set to 80% (normally 60% but thought I'd keep it a bit high just in case while were away). We left the crystal clear water on Saturday and she said she noticed the dust on the walls Wednesday and used the brush to brush it off.

I tested the water when I got home with these results:
FC = 6.5
CC = 0
pH = 8.0 (always creeps up, was 7.5 when we left)
TA = 110
CYA = 55 (I know this is low but we have a very shaded pool so keep it a bit under target)

So I added acid to bring down the pH, brushed the whole pool and am now SLAMing. BUT I want to know why did I get algae?? I never go under the minimum FC and things have been so great until now. Can you do everything right and still get algae blooms or is there something I'm missing here?? (Side note - I do remember the pool getting a bit cloudy at the same time in August last year, so something seasonal in the environment/air??)

Thank you!

 

[jblizzle]

Unless your mom was testing every day, you can't be certain that the FC did not drop too low at some point.

When do you usually test? Do you test before the swg has started generating which should be at your minimum FC?

 

[Gene Clean]

Sounds like your FC may of went under minimum for a short period. How is your salt level, and have you cleaned the cell recently? In my experience, I have only gotten slight black algae when pH is high, but this too may be a factor for you. Could of been a power outage, who knows. Since you have a vinyl, cell buildup may not be too much of a problem though.

 

[pfitz4]

I’m in the exact same situation. Would love to hear some of the responses to your question.

My pool has been sparkling all season; FC and all levels are consistently above target. Today I found a fine layer of brownish residue (assuming it’s algae) settled on the pool walls. It seemed to come out of nowhere. I tested my FC and it was 5.5 with CYA of 70.

 

[Spa Owner]

(Side note - I do remember the pool getting a bit cloudy at the same time in August last year, so something seasonal in the environment/air??)

Pools are subject to environment. Leaves, pollen, bird droppings and a myriad of other pollutants can enter the water body. As you may have noticed same thing about same time last year it is likely a plant releasing pollen or something similar that is affecting the pool. As has been mentioned it is possible the release coincided with a time the filter wasn't operating, chlorine was overwhelmed by load and algae took advantage.

SLAM should fix easily.

 

[algonquinforestpool]

Sounds like your FC may of went under minimum for a short period...Could of been a power outage, who knows.

Genius

This jogged my memory that I got an automated call from ADT security Tuesday at 8am that my system was offline = power outage. Didn't even think about the pool at the time. Power must have been off long enough to drop FC below minimum on what I remember was a VERY hot day. Algae showed up on Wednesday.

Thanks all! Love knowing there is a reason and I'm not fighting some uncontrollable algae monster.

 

[Seadweller]

The answer to your question, simply put, is yes. I've got the same issue, but I've been testing my water morning and night for weeks to find the culprit. I even raised my FC level to 10. If someone looked at my chemical balance, they'd think I had the perfect pool, but despite not one, but two successful SLAM's and perfect water balance for weeks, I still get a dusting of algae spots on the floor and walls. Circulation is the only wildcard. Other than introducing an algaecide to my routine, I'm out of options.