My in line bleach feeder lately never provides enough chlorine

[StumpedTechy]

Here are the facts.

I have an appx 20,000 square foot pool

I have an inline Pentair320 Chlorine / Bromine Chemical Feeder

Bought the pool with this unit in place it is after everything else just before the feed back into the pool.
Has worked fine for almost a year, the last 3 months it is not working.
Every time in the last 3 months I test the chlorine level is down at 0.0 and does not even begin to turn purple.
Every time I open up the unit from the top the pucks are gone and I have to add more (last two times) before 11 pucks used to last 1-2 months.
Its the same brand and type of pucks as a year ago (I bought a huge tub).
Every time I open it water does gurgle out of the line so the main tube is being filled with water.
When it was working at the 4 setting it was feeding just fine and the chlorine level was just fine. I tried moving it up to almost the 5 setting for two weeks no change in the no purple 0.0

Why is my feeder using up the pucks but my water is always testing at no chlorine unless I manually add more.
I figure I have good enough flow because the water feature is working and the water heater is not shutting off. I did clean the DE filter with a backwash last month just in case.

Do these units go bad? Do I need to buy a new one? I just figured its a tube with a flow control knob attached to it so it shouldn't ever be a problem should it be?

Do chlorine tablets go bad if left in a garage in a tub and not wet? Is it these tabs and I just need to buy fresh ones? Very confused any information you can provide would be great.

 

[Patrick_B]

If the pucks are staying dry and sealed, and I assume they are, they aren't going bad. Are the pucks being used at the normal rate they were in the past, and did you get good Chlorine readings then?

So, with those answered, what are you testing with, and what does the water look like right now?

 

[Richard320]

What test kit turns purple? You're not still using strips the way you were in September 2013 are you? You might as well swish a mouthful of water around and go by taste.

There's the slimmest chance your FC is too high and it's bleaching out the dye in the test strips.
But most likely, you have an algae bloom starting. Your pucks dissolve, but the algae eats whatever chlorine gets in the water about as fast as it hits. The reason is that while the chlorine part of the pucks breaks down in sunlight and gets used up oxidizing organic stuff, the CYA part just builds and builds and builds up. There is a ratio of chlorine to cyanuric acid that has to be maintained to keep algae at bay. You've been below it too long and making it worse by adding more pucks. Take a sample to the pool store and I'll bet they tell you you have "Chlorine Lock." It's a nonsense term, but that's what they call it when you have so much CYA buildup that the chlorine is no longer active.

 

[PoolESQ]

^^ Funny. Good post!

 

[pooldv]

My money is also on high CYA and not enough chlorine for the CYA level causing an algae bloom. Chlorine level must always be kept above the minimum level for the CYA level or algae will grow. Pool School - Chlorine / CYA Chart

 

[carpainterinaz]

I will put money on high cya as well. What your describing is exactly the same symptoms as I had after using the pentair 320 for a year. Was adding 11 tabs about every 2-3 weeks. 1 year later I was in the same boat as you are in now. I tried everything from breaking up the tabs to switching to the top feed position, before I figured out it wasn't the feeder it was the super high cya causing the 0 fc reading for 2 months. Test your cya level and drain the appropriate amount of water. And only use your feeder for vacations or if you need to dissolve a couple tabs if your cya is a little low.