Math/New Water Help

[elsie]

I apologize for the long thread but I can't seem to shorten it.

Now that I buy the bigger jugs of 6% bleach (which are much more difficult than the 1 gallon jugs to guestimate when adding to pool), I wanted to put in writing several scenarios for increasing or maintaining my pool's chlorine level for use at home, e.g., how many double cups to raise FC by about 3 ppm which is what I usually lose on a sunny day with 50-60 ppm of CYA (I don't dare go lower than this). My pool's still covered but I will be uncovering it in the next week or two so last night I ran the pump awhile and took a water sample from the skimmer. I should mention that I had a new liner installed last September and continue being perplexed why the water still can't seem to hold a chlorine level with a solid winter cover on it. I never used to have this problem with the "old" water -- it would only drop from 15 ppm to about 8 ppm over 8 long months. Anyway, no surprise when I checked last night, the CL was again at zero.

So last night I added an entire 2.46 jug of 6% bleach and let the pump run overnight; I also added yet another box of Borax as I also can't keep my pH up -- conversely with the "old" water I had to add acid because pH would creep up constantly.

This morning the CL reading was 4.5. I'm at work now and have access to the pool calculator so I plugged my baseline and target CL numbers in and hit calculate with respect to using 6% bleach. It tells me I should add 187 ounces of bleach to raise it from zero to 4.5 ppm. Yet by my math, the 2.46 jug I used would amount to 302 ounces based on 128 ounces being in a gallon x 2 + the 46 ounces = 302 ounces. I suppose it could be possible that the CL was actually higher last night and simply dropped to 4.5 by this morning which could make sense (and give me more faith in the pool calculator) but, otherwise, I'm not sure I can trust the pool calculator. Of course I suppose it's also possible the gallonage of my pool is not exactly 20,000 gal like I was told by previous owners; I was told it was 9 ft. deep but the liner installer said no, it's 8.5 feet deep. Lots of variables I guess, but what's really eating at me is why, since I got the new liner and then covered it with a winter cover just a few days later last September, I have not been able to keep chlorine in the pool or keep my pH stable all winter. I just find it very hard to believe there's an algae bloom, and the water sample I took certainly is very clear. At the cost of Borax it will be very defeating to have to add this regularly to keep the pH up, not to mention not being able to keep CL in the pool.

In the midst of my perplexion, having browsed this great forum for a number of years now, the only answer I can see for not being able to hang onto chlorine in a covered pool would be because of algae, yet it just doesn't make sense when for 6 years prior I never had these issues.

Could the pH issue be related to the CL issue? If I can't keep CL the pH drops?

I want my old water back! ;(

***By the way, as a member I could not access this forum at the same time there were issues related to the "Where are the Moderators" thread (which is closed). I have been wondering when this site might fall to never be resurrected because of the original owner MIA. Has something occurred where it is now here to stay? I know there's the Trouble Free site, but of course this forum will always feel like home to me, and I'm sure to many others, certainly including all the great Mods.***

[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.