Algae Growth with Automatic Cover?

[dmcody]

Was away for 1.5 weeks and I return to a very white – can’t see the bottom - cloudy pool. I have an automatic vinyl cover which was closed and a SWG that I haven’t had to touch all summer and have had crystal clear water since May. The SWG normally maintains a FC of 3.5 ppm. Pump runs on a timer from 8am to 11pm so 15 hours of run time per day.

I was kind of surprised that I had an outbreak seeing as it was completely covered, but we did have the hottest days of the year while I was gone +/-95 deg F. The cover tends to heat the water to a couple degrees below ambient, so I’m guessing the water temp was in the high 80’s low 90’s for a few days while I was gone.

Question 1 – With FC of 3.5 ppm, cover closed, 15 hours of pump run time, would the elevated water temp be enough to allow algae overpower the FC level? I also thought that with an opaque cover, there would be very little light to support the algae growth? Thoughts?

All of this said, I’m slamming the pool with Chlorine. Started yesterday morning with powdered shock b/c I know my CYA is low, as in Zero and thought this would be a good way to add CYA. I started with 3 bags (lbs) at 8am, then tested FC levels and added 3 more around lunch, then tested FC Levels and added 3 more around 4 o’clock. Each time i tested the FC was 0. At this point I switched to Clorox and have added to date 19 – 121 oz bottles of Clorox which is 8.25% Sodium Hypo. That’s 2300 oz of chlorine on top of 9lbs of powdered shock. I started registering FC after the first 6 jugs of Clorox. I’m slowly getting there, today I am maintaining FC 2-5 ppm above the slam level so its just a matter of time now. I’ve been backwashing frequently, keeping the cover on, and should start to see progress soon but it is still cloudy.

Question 2 – Does the automatic cover let in enough light to degrade the Chlorine? I’ve been testing pretty much on the hour and the FC is always dropping 2-3 ppm. I believe that the chlorine is still working on lingering algae growths, but in the back of my mind I just wonder if the cover is truly opaque.

Levels as of 1 pm today
FC=12.5
CC=0.5
TC=13
pH=6.8
TA=100
CH=190
CYA=0

I just added two jugs after these readings, so I’m hoping the next time I test FC, it should be around 18-20.

 

[YippeeSkippy]

Levels as of 1 pm today
FC=12.5
CC=0.5
TC=13
pH=6.8
TA=100
CH=190
CYA=0

I just added two jugs after these readings, so I’m hoping the next time I test FC, it should be around 18-20.

Were you running without CYA all summer? At first thought 3.5ppm FC seems low...except that without CYA that chlorine is much stronger as its not buffered. Yet with the cover not allowing the UV in to deplete the FC I'm uncertain what to think about your situation to be honest. When my cover is closed the FC tends to rise if not monitored so I wonder if you had algae when you closed the cover and left on vacation and it just sat there growin' away....?

Have you done something to raise that pH? A low pH like that is very hard on vinyl and will make it brittle and age faster.

No matter what happened its time to add CYA and SLAM! SLAM Process

 

[dmcody]

I had just started adding the CYA before I left, so yes it has been running at 0 all summer.

Water is clear today, lots of dead white algae on the bottom that is being vacuumed up.

I'm working on the pH as we speak, and adding CYA. pH was 7.5 before I left and I didn’t think of measuring it before I started adding the chlorine. So I was well into the slamming process with those readings.

With good levels of FC – 3.5 and the cover on I didn’t think algae could grow. Its possible that I was on the edge with algae before I left. Add in ~90 deg water in the pool overnight when the pump wasn’t running - therefore no chlorine generation from the SWG, and the algae just bloomed? Who knows, its dead now.

But final question – I have 2 main drains in the deep end that my dolphin automatic vacuum keeps hanging up on. The tops of the drain covers are ~1-2” off the bottom of the pool and the cleaner will sit flat on top of them and get stuck. Is there something I can snap onto the cover to prevent the cleaner from sitting on it?

 

[Cinic]

So if you run a SWCG pool with no CYA, is it essentially like nuking the water daily until the sun hits it and burns off the FC? Then there's little to no FC during the day and you start to build up some more when the sun goes down again?

I imagine this keep the water clear until something manages to take hold during one hot day and the demand outpaces what the SWCG can produce. I'd be curious the FC of the water at 3:00 PM with no CYA and baking in the sun all day. What time did you normally test to come up with the 3.5 number?

 

[dmcody]

Well, I work all day so its normally between 6 and 7 pm. We close the cover every night and then it depends on when the kids want to use the pool. i would imagine that some days its before lunch and some days after.