Can't keep chlorine in our perfectly balanced pool

[jent]

I'm at my wits end after dumping tons of chlorine in my pool that seems to evaporate hours later. Here are the details. 33,000 gallon plaster pool, DE filter (grids replaced end of last season), pool remodel with all new water 3 years ago. The water is clear blue. I treated for phosphates a few weeks ago thinking that was my problem when they hit 700ish, which knocked phosphates to zero, but I still cannot keep chlorine in my pool for even 12 hours. I super shocked (8 cups of Proteam Power 73 UNstabalized) at 6PM last evening after the sun went down, and by 6AM my chlorine was zero. That has happened consistently since the water warmed up to the low 70's. I switched to unstabilized powder chlorine this year after my CYA went up to 120 last summer. Several partial drains and the winter later, my CYA is back in the 40's and I plan to keep it there. I still use stabilized chlorine pucks in a float.

Not sure if this could be related, but late last summer, I used 3 packs of Poolife Mustard Algae Treatment, which is mostly sodium bromide. It was around that time that my CYA peaked and I couldn't keep chlorine in the pool the last few weeks before we closed it either. I attributed it to the high CYA.

Professionally tested results that are consistent over the last several tests over the last few weeks:
FC = .09
TC = .2
Combined Chlorine = .11 (I had a lock when I opened the pool a month ago, keeps getting smaller)
Ph = 7.7
Hardness = 225
Alkalinity = 117
Cyanuric Acid = 44 ppm
Copper, Iron AND Phosphates = zero ppm / ppb

My pool store is stumped and said they would recommend "flocking" the pool if it doesn't change. I'm not expecting it will... Any other thoughts on what could be going on or other suggestions?

[Teapot]

My pool store is stumped and said they would recommend "flocking" the pool if it doesn't change. I'm not expecting it will... Any other thoughts on what could be going on or other suggestions?

Your pool store are idiots who do not know much and therefore in my opinion should be avoided and I do not agree with floccing, but I would take them outside for a good flogging!

Not sure if this could be related, but late last summer, I used 3 packs of Poolife Mustard Algae Treatment, which is mostly sodium bromide.

It's very related, as we say, "once a bromine pool, always a bromine pool".

Basic options:
1. change it to a bromine pool, more toxic to humans and more expensive long term.
2. empty and re-fill, expensive and if your local water has phosphates and minerals you are back to stage one.
3. continue to feed it high levels of chlorine until it finally burns out the bromine. Test with a known size sample i.e. a bucket, and feed it chlorine to see how much it will take to get the bromine out and chlorine in and staying. multiply the result to work out how much chlorine you'll need to convert it back. On the plus side you didn't use too much sodium bromide.

Please let us know how you get on.

[jent]

Thank you. I can't believe three little packs of mustard algae treatment that were on sale have created so many problems that crossed pool seasons!

To do what you suggested, as an example, if I fill a bucket with 2 gallons of pool water and add 2 oz of powder chlorine, how do I know that is enough and the bromine is gone? When the chlorine stays in the bucket of water for more than a day or two?

If it does, I do the math to see how many oz of shock I need for 33,000 gallons? If i'm doing the math right, 2 oz of shock for 33,000 gallon pool would be 4,125 cups of shock? lol. That can't be right. Do I need to go back to math camp?

[Denniswiseman]

Seconded what Teapot says
Forget the pool store and only put in what you need not what they tell you
Get yourself a decent FAS/DPD test kit (Taylor K2006c or TF Testkits TF100) and do your own testing and lets see your numbers
FC:
TC:
pH:
TA:
CH:
CYA:
Adding pucks or powder adds additional CYA or Calcium
For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.
For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.
For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by at least 7 ppm

Use these common products to balance and sanitise your pool
Liquid chlorine (sodium hypochlorite or plain bleach)
Muriatic acid (hydrochloric acid) to lower pH and TA
Bicarbonate of soda to raise TA
Aeration will raise pH only
Soda ash will raise pH and TA

With a CYA of 44 you need a Slam level of 18 as recommended in Chlorine / CYA Chart

[jent]

Thank you. I have a Taylor K-2005 complete kit. I have run the tests a few times to make sure i'm doing them right and i'm getting consistent readings as follows:

FC: barely registers any color
TC: somewhere under 1.0
pH: 7.4
TA: 120
CH: 220
CYA: I can still see the black dot at the bottom of the tester when it is filled to the VERY top, which means less than 20. This is different from what the pool store tests said (=40). I repeated the test 3 times to confirm.

Also, two new developments with the pool water. 1.) it is cloudy and I can't see the main drain (at 8.5 feet) 2.) while doing the water tests sitting beside the pool, I noticed dark spots peeking out from the underside of the ladder steps in the deep end. I looked closer and couldn't tell what it was so I removed the ladder and put it on the deck. The entire bottom side of each of the ladder steps is covered in a black/dark brown slimy algae. I added a pic (warning: it is ugly!)

algae.JPG (159.94 KiB) Viewed 2848 times

Given the discrepancy in my CYA level test from the store (mine shows next to nothing vs theirs that said 40) and the fact that i had nasty, active algae growing on the underside of my ladder steps, I'm wondering if that is at least a big part of my problem of not being able to get any FC in my pool. I am thinking that I should add an X-large amount (starting with 5 lbs) of stabilized chlorine at sunset and test hourly to make sure it is "holding" and keep adding more until I get a reading of at least 10PPM. That will also add the necessary CYA.

I shocked the pool again mid week and even 1 hour after adding 4 pounds of UNstabilized chlorine, I was not reading any free chlorine. I think i need CYA to get me to at least in the 40s.

Does this sound reasonable and like a good plan?

[Denniswiseman]

Sounds reasonable and a good plan
We don't normally recommend stabilised chlorine but in this case it would be the best thing to get your CYA up to a decent level which you can then decide on the shock level to maintain with regular testing and liquid chlorine (plain bleach)
Algae will eat up a load of chlorine, don't forget to brush and get into the parts that are hidden (light niche, steps)
Keep refering to the Chlorine / CYA Chart and the Recommended Pool Levels
Be careful you don't overdo the CYA as the higher it is the more chlorine will be needed

[Teapot]

Hi Jent, IMHO you need to treat a bucket full of pool water with liquid (un-stabilsed) chlorine first to see what it will take to get the water back holding chlorine. This could save you more time and money and let you decide if the water change is the best route or not. It's now a bromine pool, the normal levels of chlorine are just converted into sodium bromide so you need to go high on the chlorine and hold it there until the water can hold the chlorine. Using stabilised versions just reduces chlorine's efficiency at this point.

Ladder, those are plastic treads and the news is black algae isn't an algae!! Yet another thing the pool industry has got wrong, they won't correct it because it leads to more sales! Black algae is actually a cyanobacteria it is clever enough to take up residence in plastics and plaster being almost chlorine resistant. If you can't get new ladder treads, get a new ladder. You can try treating the bacteria with strong chlorine dioxide if you can find some, maybe treating with germicidal UV may help (not tried UV) but the cyanobacteria can lay almost dormant and re-appear if conditions become favorable again.

[jent]

Good to know on the ladder treads. Just ordered new ones. I was shocked to see it had already grown back while sitting on the deck all afternoon, after washing it with a strong muriatic acid solution!

I am afraid you are right Teapot. Despite wishing the stuff growing under the ladder treads was eating my chlorine, the bromine from last season seems to be the problem. I nuked the pool with 5 lbs of chlorine late afternoon yesterday and proceeded to add 3 more pounds before going to bed when it barely registered 10ppm, and there was zero FC this morning. One upside, my CYA is now a respectable 40. I just drained 6ish inches so it is well below the skimmer line. This will be the second partial drain below the skimmer line since I put in the bromine last season plus a few other backwashes and post heavy rain drains. I really hope this does the trick so I can finally keep some chlorine in the pool.

If this doesn't work, I guess I'll drain it again even more and pay for a truck to deliver water to re-fill. I'm on a well so I have to re-fill with a hose a few hours at a time and it is a major pain in the rear and takes forever. I am SO mad the innocent looking little $3 yellow algae packets at my hardware store created such havoc last year and still this year! There was NOTHING on the package that talked about the consequences of using that in a chlorinated pool, which is probably 90% of the pool population. I called the manufacturer and registered an official complaint. Lesson learned.