Back to chemistry class...

[Donna's Poolboy]

Rats! Just when I thought everything was great, I've hit a snag. Crystal clear water after the initial open, then we had a chilly spell here where we didn't use the pool for 3 days (covered for all 3). I added a jug of 6% bleach each day which was my routine from last year, but when I pulled back the cover tonight...cloudy water! Here's my numbers:

FC 0
CC 0
ph 7.2
alk 160
cya 70
cal 220
times my 3 year old told me "dad...that water's DIRTY" 62.5

Obviously, there's no chlorine in the water and I noticed that my ph (which was stable at around 7.6) had fallen to 7.2. After thinking about it and poking around in other posts, I have a GUESS as to what I did wrong:
After first opening the pool I raised the water to shock level (20 ppm) and waited for it to clear up (which it did in about 4 days). However, I probably didn't keep it at shock level long enough. Does that make sense? That's about all I can come up with. The water is cloudy but not green.



Here's my plan:
I added a bunch of bleach and took the cl back up to 20 ppm.
I'll keep it at that level for 2 or 3 days or until there's no drop off overnight. I didn't add any Borax yet...it was stable so I'd hate to screw with it too much. I figure I'll tackle the chlorine problem first then see what the ph looks like afterwards. Will the ph come up after you shock the water?

[CarlD]

OK,
pH of 7.2 is a little low but not so low you need to worry. In fact, chlorine will be more effective there. I'd leave it for now.

Yes, keep your FC at 20--check it two to three times a day, vacuum everyday, preferably to waste, and brush it everyday. If you have an robotic cleaner like a Dolphin or Aquabot that climbs and brushes the walls, you can use that to vacuum and brush.

Otherwise your plan is fine.

When you "get there", if pH is still at 7.2, try raising your pH by aerating the water rather than adding Borax as your T/A at 160 is a little high (but still OK for vinyl) and will otherwise go up even more as pH rises. Only raising pH by aeration will prevent that.

Aerating can be just by leaving the pool uncovered, adding a sprayer or fountain, or a gang of splashing kids--but the last is ONLY after the water is sanitary again.

[mbar]

Just a note, sometimes keeping the pool at shock levels for a couple of days is not enough. You must check at night and see if you are losing any chlorine overnight, because sometimes even with a cc of 0, if the pool is using chlorine overnight, then it is fighting something that will take hold if you don't get rid of it completely. I have had to keep my pool at shock for 6 days so far after opeining. My water is clear, no combined chlorine, but still losing some chlorine overnight. Each night it loses less - so I think it is almost ready!!

[Jeffski]

Aerating can be just by leaving the pool uncovered, adding a sprayer or fountain, or a gang of splashing kids--but the last is ONLY after the water is sanitary again.

Are you saying you wouldn't let kids swim with the FC down to zero?

[Ohm_Boy]

Are you saying you wouldn't let kids swim with the FC down to zero?

Well, I sure wouldn't. With a zero FC, there is nothing sanitizing the water. Maybe it *JUST* hit zero a few seconds ago, and nothing is alive in there, but more likely it's been at zero long enough for some serious bacteria to grow.

Either way, once the bird droppings hit, and whatever airborne nasties settle in from blowing over the neighbor's trash cans, and swimmers start tracking in dirt and GodOnlyKnowsWhatElse, you have an unhealthy bacteria culture situation in a hurry.

Remember that it's not just about algae. Its about sanitization.
Algae is just nature's way of trying to keep you out of an unsanitary pool.

[chem geek]

Bacteria have a generation rate, which is the time it takes to double in population, of from 15 minutes to an hour depending on species and conditions. If it's 15 minutes, then in 8 hours 1 bacterium may become over 4 billion bacteria. Even if it's the generation rate is 1 hour, then in 24 hours 1 bacterium may become over 16 million.

[EDIT] Algae have a generation rate of from 4 to 8 hours which is why it seems like it takes a while for algae to appear, but it grows (in ideal conditions) by a factor of 8 to 64 over a 24-hour period. So it seems like it starts out more slowly, but then appears to "bloom". [END-EDIT]

Richard

[Jeffski]

So a pool that has dropped to zero chlorine can be more unsanitary than a lake within 24 hours?

[Donna's Poolboy]

Here's an update...
I lost about 6 ppm of chlorine overnight and the ph remained at 7.2
The water is MUCH clearer (can see the drains in the 8' end and the liner pattern) but still somewhat cloudy.

Each jug of 6% bleach raises my cl by 2 ppm, so I added 3 jugs and I'll check it again later today. The pool is in full sunlight for the rest of the day.

I should have mentioned that all the heavy debris has been vacuumed out (to waste) and I brushed the walls several times right after we opened a couple weeks ago. The only sediment on the bottom is the minimal stuff that will collect around the seams opposite the return jets overnight. Should I still vac to waste?

Looking ahead to the aeration part...we've got a couple fountains at the deep end. We usually only turn them on when the kids are swimming. But if I leave them on for a good portion of the day, that will aerate and raise the ph?

Thanks,
Bill

[chem geek]

In "ideal" conditions with proper nutrients in the water and depending on the bacteria, then yes. In a lake, or any ecosystem, a balance gets developed between many different species. So the bacteria are kept in check by protozoa, algae and similar microorganisms all competing for the same food (nutrients) and there are various species that have defenses against each other. There are bacteria everywhere -- millions of them on even a small patch of your skin. The problem isn't in having lots of bacteria, the problem is having lots of the WRONG bacteria (or protozoa or viruses).

In pool water, the wrong bacteria is usually that associated with fecal matter. This includes various common strains of E.coli but also includes pathogens associated with disease including viruses. Though it's not a pleasant image, you really have to think of an unsanitized pool as a toilet bowl (whereas a sanitized pool is clear and clean water). In a lake, river or stream, the various organisms tend to self-clean or at least keep in balance what is dumped into them, but they can certainly be overwhelmed. For example, cholera is caused by a bacterium and can readily be spread even in "open" waters as this was a real problem in India (most people know about the "wells" in England, but those were not open waters). There's an interesting account of this and other cholera outbreaks at this link.

The reality is, however, that the risk of getting disease from even an unsanitized pool is low. It's just that sanitation reduces the risk to near-zero, at least for the easy-to-kill pathogens that low levels of disinfecting chlorine takes care of. The biggest risk in an unsanitized pool is transmission of disease from person to person which is why most serious outbreaks are in commercial pool environments where there are heavy bather loads (i.e. lots of people) rather than residential pools. In a residential environment, the most common problem is with hot tubs where the bacterium that causes hot tub itch is not uncommon and takes somewhat higher levels of chlorine to kill (so using Dichlor exclusively in a hot tub is not wise, even though that is often recommended by the industry).

Richard

[Donna's Poolboy]

PM update...
lost 6 ppm through the day and the ph stayed at 7.2
I took the cl back up to 20 ppm at around 6:00 pm. It's 10:00 pm now and the cl is still at 20 ppm. The water has very little cloudiness, but not quite crystal clear--I'd call it a 95% improvement over 24 hours ago.

I'll post new numbers in the morning.
This is exciting stuff!