Clear, but no chlorine???

[mary jo]

OK- overnight test results are not so good for some reason.
I decided to use the 10ml sample since I now have enough product.
tested last night @ 11:00 FC=35 CC=3

tested this morning @ 7:15 FC=30 CC=3

Is a hiccup like this common? I repeated this morning's test 3 times to be sure.

[CarlD]

Dropping from 33 to 30 overnight? Perfectly normal! when you are super-shocking it's harder to maintain the FC...and you only dropped 9%. I wouldn't worry about that at all.
What I'm wondering is why your CC is so high and not dropping with FC > 30.

PS: I'd run the FAS-DPD test using the 5ml line instead of the ten. If you don't have that line you can either guess where it is or use a kid's med cup that comes with cough medicine with a 5 ml line. Each drop then is 1 full ppm rather than .5. It will take less time to do the test, use half the R-0871, and certainly be accurate enough at those high FC levels.

[BigDave]

I pretty much agree with CarlD, the FC loss is not such a big deal but the CC consistent at 3ppm.
Two questions:
How much bleach did you use yesterday?
Is there any chance that a bromine product has been put in the pool.

[mary jo]

OK- it was actually a 5ppm drop (35 down to 30). Did I wait too long to take the morning test? (should I test before sunrise ~ 6:00?) Yesterday is was overcast and rainy all day. This morning it's sunny.

I added 1 1/2 jugs yesterday. Yesterday morning's initial reading was 35 so I didn't need to add much to keep it at 30. I added the last jug @ 9:00 and tested at 11:00 and got 35.

Not sure what bromine is, but the only chemicals ever put into my pool this season: pH up (about 15 lbs), phos-free (1.4L) and 3" chlorine tablets for the inline chlorinator.

[CarlD]

It's still not a big change--if it dropped from 35 to 20 or 15 we'd be concerned, but from 35 to 30? That's OK.

Bromine is an alternate sanitizer to chlorine. It's more expensive, has a number of drawbacks, but is much more resistant to heat in hot tubs. It also doesn't "play well" with chlorine.

pH Up! is nothing more than Sodium Carbonate, aka Washing Soda, just overpriced.
3" chlorine tablets are Tri-chlor tablets--if they are 99% they are good. But for every 10ppm of chlorine they add, they add 6ppm of CYA/Stabilizer, plus push pH down.
Not sure what's in the Phos-Free, but I doubt there's any bromine in it.

Combined Chloramines can be all sorts of chloramines, not just the one bromine mixed with chlorine produces (monchloramine?) All kinds of things can be metabolized to form them, but guessing which one(s) caused the CC=3 is beyond me.

[BigDave]

1-1/2 jugs of 8.25% in 15,000 gallons is a daily chlorine demand of about 8ppm which still seems high to me.
I asked about bromine because bromine can create a permanently high chlorine demand.
I will put together another summary of this thread later today and ask PoolDoc or Richard to take a look.

For now, I'd maintain shock.

[PoolDoc]

Just checking in on this thread; obviously some good progress has been made.

But I have a couple of suggestions.

1. Unless you know of some reason not to do so, remove the Nature2 cartridge, even though it's old. ANY cartridge or filter media is a potential reservoir of accumulated oxidizable 'goo'.

2. For the same reason, clean the filter cartridges. Be sure to do it correctly. Spraying them off (with the hose; NOT with a pressure washer!!) is a good intermediate cleaning, but a full cleaning, which should remove any oxidizable 'goo' that could create chlorine demand takes more. See http://pool9.net/cart-clean/

3. It wasn't clear to me whether you ever inspected light niches or other recessed or hidden areas in the pool. If there are any such recesses, and if it's at all possible, inspect them. It does happen that such locations will fill completely with live 'slime'. Physical cleaning is required; otherwise, the slime will just 'recover' when chlorine levels drop.

Good luck!