Math/New Water Help

[CarlD]

Well, we cannot tell from just one number.

We need to full set:
FC
CC (or TC)
pH
T/A
CYA (stabilizer levels)

Also, don't sample the water from the skimmer, sample it from a fairly innocuous part of the pool.

AS A W.A.G. (Wild "Absurd" Guess) I'd guess your CYA is 0 and you have something growing and it's "eating" your chlorine down after you add it.

[waste]

Hi Elsie

As I was reading your post, the thought that "the cya is gone" popped up a couple times -- I AM CERTAINLY not anywhere near as knowledgeable as chem_geek nor waterbear, but, IF memory hasn't failed me - when the cya gets eaten by the dirt bacteria (?) the result is ammonia which causes a HUGE chlorine demand, and would exacerbate the loss of cl due to UV.

I can't say what net effect this would have on the pH, but something in the back of my mind is saying that it is also a result of having the cya consumed ??

With respect to TFP, IMHO, something HAD to be done when this site stopped accepting new members and Ben went MIA I've said it before and caught BS for it but, I will always!! call this site my first stop when I get home and can get online! I give Ben credit for advocating BBB and his 'debunking' of widespread pool industry practices, beliefs and 'general screwing of customers'!!!! Without this site, and Ben's unannounced departure, TFP wouldn't exist!

As Al said the other day, 'It's nice to see Pool Forum being active again!' As long as the site exists - I'll be here, the mods will be here (computer servers allowing ) and I would hope that all members will stop by from time to time - even if it's just to say "HI" and let the world know that PF is still an active site

[chem geek]

I don't think this is a situation of the soil bacteria getting into the pool and converting CYA to ammonia. It doesn't sound like the CYA dropped and in this case chlorine is getting measured -- it's just getting consumed faster than one would expect. When you have ammonia in the water, the chlorine gets consumed almost immediately -- I measured zero chlorine just 30 minutes later in my own pool when this happened to me.

To get an idea for how much chlorine might be needed until the water becomes stable, one can do a bucket test. Take a large bucket of pool water and add chlorine to it at a shock level. Measure the rate of decline in the FC and also note how much chlorine it takes until the FC holds when out of the sunlight.

Nevertheless, Carl is right that you should test all your water parameters, including CYA, since that's the only way to really know what to do next. If the CYA is at zero, then that would explain a huge drop in FC during the day, though it shouldn't drop much at night unless there is algae growth or something else consuming the chlorine.

Richard

[elsie]

Hi Carl, Waste and Richard,

I know better than to *not* post all the salient numbers, geesh! Here they are as of last night:

CL 4.0
FC 4.0
TA 220
pH 7.5 (having added box of Borax)
CYA 50-55
Solid winter cover still intact

I now remember that when I had the new liner install in the Fall I kept the pool open just long enough to put stabilizer in and get it in the 50 ppm range along with, as I vaguely recall, about 5 ppm of CL -- I didn't shock as it was a brand new liner and I didn't want a high level of CL for the 8 months it was covered/closed as in the past I lost only about half the CL over 8 months with the winter cover on. So the CYA level has held but the CL has not.

My Alk is high. Typically it runs around 180 without any issues, not even cloudy water. I just perused the Stickies on lowering Alk (by lowering pH and aerating) and have printed. Although I don't have any kids or fountains, will it be sufficient to turn my two jets upward to create air bubbles? In any event, this will have to wait until I uncover the pool. At that time I will also give the water it's first shocking. Frankly, in years past I never tested for TA during the winter/covered months and for all I know it was always much higher then but then perhaps fell to its set-point of 180 with a small amount of aeration going on from the jets and my own daily laps.

So I suppose I could wait a stretch and see if the TA naturally falls or I could manipulate through the proven process. Is the latter preferred or is there little harm in just observing the pH and TA for a stretch?

I won't worry about the CL right now, as shocking it when I uncover it should resolve any issues. If there is some (invisible) algae and doesn't test out as CC or tinted water (it truly is as clear as it can get), I'm thinking one shock instead of keeping the CL at shock value for an extended time should be appropriate? As you can see I am a trifle nervous about subjecting the new liner to high levels of chlorine. Of course, how stable the chlorine level is after that will tell me a great deal and probably answer this question itself.

It looks like I won't be opening until the weekend after this upcoming one because the trees are in their final fit of shedding little oblong gifts that rain down which can clog the impeller. I'll report back and let you know how this all goes.

Thank you everyone for your input, as always. And Waste, good analysis of PF and how it relates to TFP (which I once registered with but have never posted as PF is where my mouse continues to take me) and this forum's incredibly rich history - and what could be called its living legacies. I, too, am still thrilled it continues -

Elsie

[CarlD]

You should be seeing the chlorine demand going down if that's your CYA and there's no CC.

Just aerating your water won't lower your T/A. You have to add acid to bring down both the T/A and pH. Then, when you aerate, it raises the pH without raising T/A, which even Borax will do. It's a racheting effect.

[elsie]

Yes, there should be zero chlorine demand with the winter cover and still quite cold water -- unless there's algae. And I'm thinking more and more that may very well be the case despite the clarity of the water. I understand that the pH has to come down to have the aeration process work effectively having printed out the Stickie information. But since the pH is not stable it may very well come down on its own between now and when I uncover the pool.

This brings me back to a question higher in this thread -- what makes the pH continue to drop? Does the answer lie in my high TA? My goal, of course, is to not have to continually add Borax which would impact the economy of the bleach method.

[chem geek]

As you point out, usually the pH slowly rises when using bleach or chlorinating liquid. Usually, the pH only drops when using Trichlor or Dichlor or when using non-chlorine shock (MPS). It will also drop when chlorine goes from a high FC to a lower FC. The pH will drop some going from colder water temperature to warmer water temperature -- going from 45F to 80F would drop the pH from 7.5 to 7.2 (with your TA and CYA levels).

Usually with the higher TA such as you have, the pH will tend to rise if the pool is uncovered (or has a mesh cover) so can outgas. Unless your CH is high, I wouldn't worry about your high TA right now until we sort out the pH drop. You'll want a higher TA to help compensate for that if we can't otherwise figure out why the pH is dropping.

It's possible that the new liner has some sort of reactive chemical on or part of it and this is leading to greater chlorine demand. It's possible that this chemical might also be acidic leading to a lower pH when getting into the water. However, I've never seen anyone report this situation before and it seems odd.

Richard