Extended SLAM and OCLT not really improving

[enoshixi]

So I am a long time TFP'er. I had an above ground 15,000 gallon pool for years and maintenance was a breeze. It consumed about 2ppm chlorine a day which I add via 12.5% liquid chlorine. Fast-forward to today and I have moved to a house with a 30,000 gallon in-ground vinyl pool. The pool regularly consumes 5+ ppm of chlorine daily and seems extremely susceptible to algae in spite of maintained chlorine levels. I have gone through several SLAMs, they always go on much longer than I would expect and never really make a dent in the chlorine demand. My gut says I've never really completely wiped out whatever nasties are living in the pool.

So I've currently been SLAMing since 7/11 and have yet to pass the OCLT. Current numbers (taken with TF-100):

FC: 16
CC: 1
PH: 7.2 (before starting SLAM)
TA: 180
CYA: 40
CH: 440 (it has admittedly been a while since I tested this one and I suspect it is lower now)

And my recent OCLT results:
7/15 lost 3 ppm
7/16 lost 3 ppm
7/17 lost 2.5 ppm
7/18 lost 1.5 ppm
7/19 lost 2.5 ppm

It is discouraging because I feel like I'm not making any progress. I thoroughly brush every surface daily. I've removed the light and scrubbed the niche. I've scrubbed under the ladder and inside the skimmers. I've opened up and hosed out my DE filter. I've even taken a toothbrush and scrubbed around the seams where the steps meet the liner. The last few nights I've vacuumed, skimmed, and emptied my skimmer and pump baskets right before bed to eliminate any debris from interfering. Pump has been running 24/7. My reagents are fresh. The water has been clear and sparkling since 7/14.

So what is the deal? Does this seem excessive or am I just getting impatient? I am using about 3 gallons of 12.5% liquid chlorine a day.

I know the previous owner didn't maintain the pool very well (it was bright green in the listing pictures!). My fear is that there is some biofilm or something hiding in the plumbing that the chlorine can't fully break down.

 

[duraleigh]

If you are consuming 3 gallons of 12% daily in a 30k pool that's 12 ppm and that doesn't really make sense in a pool you say is crystal clear and only is losing around 2 or so ppm overnight.

could you confirm that 3 gallon consumption?

 

[enoshixi]

Yep, about 3 gallons. I've been adding 1 gallon in the morning before work. In the evening FC has been around 8 ppm, so another 2 gallons to bring it back up to 16. And no exaggeration at all, the water is clear and sparkly, it looks perfect.

 

[jblizzle]

Please add your location (City, State or City, Country) to your profile and pool details to your signature as described HERE as it will help us help you.

Also, try cleaning your chlorine test tube out REALLY well. Been a few reports of lingering CCs that seem to be due to a dirty vial.

 

[enoshixi]

Ok, city and signature should be there now. Anything special to clean it with? I always rinse it out with pool water 3 or 4 times prior to collecting a sample for testing.

 

[jblizzle]

Not sure. I think some have rinsed it with some bleach really well and another just mechanically rubbed everything down with a wooden dowel in the corners which seem to be enough

 

[duraleigh]

I can't make that consumption of FC make sense. You are losing roughly 10 ppm FC during the day in a crystal clear pool with 40 CYA in Minnesota.....and then another 2-3 ppm overnight.

I have never seen anything like that reported and I am stumped for an answer.

 

[pabeader]

Are there sources of organics that can blow into the pool?

 

[enoshixi]

I can't make that consumption of FC make sense. You are losing roughly 10 ppm FC during the day in a crystal clear pool with 40 CYA in Minnesota.....and then another 2-3 ppm overnight.

I have never seen anything like that reported and I am stumped for an answer.

You and me both. We have had an especially hot and sunny streak of days. Up until yesterday, which was cool and overcast/rainy all day. And perhaps not coincidentally, my chlorine usage dropped dramatically yesterday. When I checked in the evening, FC was at 12 instead of the 8 I had been seeing. OCLT was 1.5 last night. Hopefully the cooler cloudy weather is giving me the edge I need to win this battle.

Are there sources of organics that can blow into the pool?

Yes, plenty. Lot's of trees that drop debris all summer long. We also have a pond near by and small frogs and toads trapped in the pool pretty frequently. They are always much worse when it storms, I tried counting one time and lost count around 50. But the weather has been nice lately so they have been pretty minimal while I've been SLAMing. Plus I've been obsessive about scooping them out to keep them from interfering with my OCLTs.