Chlorine lock - need to drain pool?

[DonnaElvira]

Hi – I’m new to this website, and new to pool maintenance. Before I get to ‘the problem’, here are some basic facts and history:

19,100 gallon pool (cement + pebbles), 6 years old; System 3 Modular Media Filter, Polaris pool-sweep.

Acquired by us 4.5 years ago. Since then it has been looked after by the same private-contractor pool guy (let’s call him Tom). Tom told us that the Nature 2 Professional G Inground Purifier that the previous owners had installed is unnecessary, and that it is better to just use chlorine. He comes once a week in the summer and once a fortnight during winter to test the water and adjust the chemicals. He also put in one of those little floating baskets with chlorine tablets. He cleans the filter once a year (when asked about this, he said that the filter works better if it is cleaned only once a year).

So basically we left him to it, but it seems that we now have a problem. Tom says the pool suffers from chlorine lock and will probably have to be partially drained and refilled. I have spent considerable time reading on your wonderful website, but even though I now know a little more about pool chemistry, I am getting more confused by the minute.

Tom added chlorine on Tuesday, but I do not know what the test results were then (other than he told me that the chlorine is neutralised very quickly and he keeps having to shock the pool really hard). I had the water tested at a local pool store on Thursday and was told that total dissolved solids = 2.1 (apparently this is high - should be 0.19 max?); pH = 7;
Chlorine = 3; CYA = 90-100.

I bought a kit and re-tested some of this today: Free chlorine = 1.5 (unchanged when testing for TC); pH = 7.3; T/A = 60. By the way, the water looks clean.

The water was very warm but since the solar heating was turned off four days ago it has cooled down considerably (sorry, don’t know the temperature – just noticed the thermometer is broken…). We are in California – 90+ days are the norm at this time of the year.

I would be very grateful for any suggestions. TIA!

[CarlD]

I was liking Tom until he said "Chlorine lock". No such thing. Go to the Best Guess table and you'll see that for 90-100ppm of CYA (stabilizer) you need to keep your chlorine at 8 to 10ppm, and shock it at 25. That's all, and you do NOT have to drain. If you drain half your water and refill, your CYA will be 45-50--and you STILL shouldn't use tablets then either--they add CYA.

That's fine, but you can't use the floater with the tablets any more. Use Liquid Chlorine or laundry bleach (same thing) for you chlorine--it won't add CYA.

[DonnaElvira]

Thank you - but please bear in mind that you are dealing with a complete novice without any knowledge of chemistry...

I have searched around on the forum, but I'm still not sure. To get the chlorine level to 8-10 ppm, do I need to add about 1.5 gallon of household bleach? Should I do this in the evening, but while the pump is still running? (I already removed the floater.)

Thank you for your patience!

[CarlD]

Sure, you'll do fine.

At the top of the Chlorine and Chlorination topic, and the Testing topic, there are stickied threads on b-b-b, Best Guess and Newbie chemistry.

They should help.

1 gallon of household bleach (5.25%) will add just over 2.5 ppm of FC. 1 gallon of ultra (6%) will add 3 ppm of Free Chlorine (FC).

1.5 gallons of regular will add just under 8ppm. 1.5 gallons of Ultra will add 9 ppm.

[waste]

Donna, welcome to the forum, it'll get easier as you read and learn. Carl is, of course, right about the bleach concentrartions and gauging the addition by that. Something that isn't usually mentioned is that the perameters we shoot for here are broad enough that adding a little more or less will put you in the desired range, and , if you don't have a problem (if you're a little over or under what's suggested) then there is no reason to add more 'stuff' to your pool. Every pool is unique and as such has it's own chemical requirements - if you stay close to what is advocated here, you will most probably have no problems!
Go ahead and dump your 1 1/2 - 2 gal of bleach in the pool and I'll lay odds that you'll be ok If you have more questions, don't be shy about asking (and give the forum a good read and especially Poolsolutions. com [the site that mothered this one])

[duraleigh]

Donna, I suggest you shock your pool....1.5 or 2 or 3 or 4 gallons won't do it.

Download mwsmith2's bleachcalc from any of his posts...you'll use it all Summer.

What it will tell you is that to shock a 19,100 gallons pool with a CYA of 100 and with a current FC of 1.5.....you're gonna' need 7.5 gallons of 6% clorox.
Any less and you're tap dancing around your issues instead of stomping on them.

Now, since the large jugs of clorox are 1.42 gallons and you have a plaster pool, I suggest you put in 6 large jugs...all at once. That will raise your Cl to 28ppm (no problem) and will start to cure "chlorine lock" (which doesn't exist).

I suggest you put it in at dusk to be most effective and then test again the next AM before the Sun hits it. I'll bet money your gonna' lose a lot of Cl that first night. If so, you need to repeat the process the next evening and again the next. bringing your Cl up to 28ppm each evening.

When you hold Cl overnite (less then 2ppm loss) you can be assured the organics are cleared from your pool and you will start using far less chlorine. Maintain it from 5-10ppm from that point on.

What I think Tom is struggling with is not putting enough Cl to get to breakpoint. Without getting into details, if you'll put in those 6 large jugs, you will get to breakpoint and your pool will return to it's healthy condition.

PS- disregard TDS....it's normally not important and that test result was bogus, anyway.

Tom will probably be reluctant to follow this path and you'll have to make a choice. The one we're recommending here on the forum will fix the pool.

[Poolsean]

I agree with Dave and Carl...
CHLORINE LOCK is just another way of saying
"somethings using up the chlorine and I have no idea what"
...IF this is the case, basically you have a high chlorine demand that must be satisfied first, thus the need to superchlorinate as Dave recommends.

However, I don't necessarily think there is a problem other than your chlorine residual is probably a little low for your cya level maintained. You did mention that your water looks clear and this is good. What does your calcium hardness level look like?
BYW....what kind of test kit did you use?

[DonnaElvira]

The kit I'm using is a Premier Poolmaster; the CYA test kit is also by Poolmaster.

I'm embarrassed to say that I do not know how to test the calcium hardness level... (NB: Will read up on Ben's Kit straightaway!)

When I first posted I only had a gallon or so of bleach to hand. The morning after the figures were almost unchanged.

Today I finally managed to get to Wal-Mart to buy more bleach, so am planning to shock tomorrow evening.

BTW, the pool still looks very clean

PS: What do I tell Tom when he comes to do his bit on Wednesday???

[ThePoolGuy]

Chorline lock....Now that is funny I'm with PoolSean on that one!


As for what to tell Tom on Wednesday, I wouldn't agree to drain the pool for one thing I would most likely go along with him until I learned a little more about doing your own pool. That is if you got time to clean the pool your self. It's really not that much time consuming once it's under controll. If you don't have time, you can work with Tom to help him understand whats going on or find a new pool guy.


Best of Luck
ThePoolGuy

[aylad]

At some point, you're going to have to either start caring for the pool yourself and get rid of Tom, or let Tom do it his way. If you're already taking care of it, why do you need Tom?

I would be interested in what form of chlorine he's adding--I'm guessing he's shocking with dichlor, which is raising your CYA every time he adds it. If that's the case, I'd stop him now...........

Janet