How long for Cl to disappear?

[cygnusecks]

I have a new 14k IG ptec pool. I have balanced the chemicals and I have about 50ppm of CYA. The pool is enclosed by a screen enclosure. It is a free-form pool with a large baja shelf and swimout and spa.

Question: how long would 3ppm of Cl take to go down to 0 (or where it no longer registers). For my pool, I have noticed that it takes about 2 days to go from ~3.0 to 0. is this fast/slow? I feel like I'm constantly bouncing the Cl level from 0 to 3, waiting for it to hit 0 again, and re-upping it to 3. I think this is the wrong approach but I will quickly run out of reagent if I test 3x or 4x a day. Should I add more CYA, and will it help me maintain a better level of Cl (say, 6-7 ppm) ?

[Watermom]

With a cya of 50, you shouldn't be letting your cl drop to 0. Actually, you should be keeping it between 3-6 all the time. As long as you aren't having any algae, etc., you only need to be testing in the evening. Then, add enough bleach to take your cl back up to 6. I would not add any more cya. We generally recommend cya between 30-50. What type of chlorine are you using?

http://www.poolforum.com/pf2/showthread.php?t=365

[cygnusecks]

I am using regular bleach - either clorox or generic "publix" brand (publix is a regional grocer here in the southeast). I buy the big 1.42 gal size, and dump half of it in every other day, which seems to get me to 3 or slightly higher.

Here's another question: Will a full jug of bleach take exactly 2x longer to dissipate than half a jug, given the same weather and exposure and same pool, and all other chemicals being balanced, and no additional chlorine demand? I don't think I have *any* algae, as I can't see any, and no slimy surfaces.

[brent.roberts]

Hi

You could have some stuff in the pool that is using up the chlorine.

The key to discovering that is to know you free chlorine ( FC ) and total chlorine ( TC)
Subtracting them will give your combined chlorine ( CC )

If your CC is greater than about 0.5 then you have something in the pool that needs to be shocked out. And this could be why your levels seem to be running up and down a lot.

Can you test and get us those numbers ?? We could give you some better comments if we knew that.
When the pool starts to smell of chlorine it is also a sign of high CC. The smell, strangely goes away when you add more chlorine in a shock treatment.

[Watermom]

Plus, remember, even a 'clean' pool will use chlorine. You don't expect your chlorine levels to be unchanging.

[cygnusecks]

The drop kit I have from Walmart I'm not sure I trust to measure CC. You have to measure FC by dropping 5 drops of OTO, then reading within 10 seconds to get FC. Then, after 2 minutes it "fully develops" and you can read TC. Each time I've tested, the water has never "developed" more after the initial 10 second wait, so either I have no CC (which is odd; we've been using the pool and the dog gets in there constantly) or the test is bad. I'm waiting on my PS234, which I hope has a better way to measure CC.

I'm still interested in knowing whether bleach dissipates at a constant speed, given all other variables are the same. That is, will a full jug of Cl be gone in twice the time as half a jug? Or is there a level of Cl which, when reached, will tend to stay in the pool longer?

[waterbear]

OTO, the reagent in the walmart kit, is NOT an accurate way to test for FC. If you can read the test in the first 2 or 3 seconds you might get an idea if the was a large enough difference in the FC and TC. The color blocks on the comparator just don't have the accuracy to measure .5 ppm difference in the levels. It MIGHT be possible with a colorimeter.To test for FC you really need a DPD or FAS-DPD test for any kind of accuracy.

As far as your second point on how long it will take the chlorine to dissapate...I don't really know but it seems that a higher concentration would dissapate at at faster rate (similar to the way that stronger concentrations of sodium hypochlorite lose strenth faster than weaker ones) because of the instability of sodium hypochlorite. It is the FC in the solution that you would be loosing so I don't thing the amount stabilized by the CYA would have much effect. That is why you need to have a higher FC level when your stabilizer level is higher...so there is an adequite amount of available FC in the water.

Like I said, I really don't know for sure but it seems that this would be the case to me.

[Poolsean]

"which is odd; we've been using the pool and the dog gets in there constantly"
Ummmm, did your chlorine drop while the dog was kept out of the pool or with the dog going in every day?
One dog can consume copious amount of chlorine! However, if you've kept the dog out and your chlorine is still dropping, you have a high chlorine demand in your pool. Combined chlorine is one source, and as suggested by Brent, OTO is a terrible test kit to use for this test.