Chlorinating Guidance Sought

[Coconuts]

Hi; I just joined, and while I have spent some time reading through forum posts and educating myself, I have some special circumstances, and would appreciate some advice on the best way to maintain FC levels.

I have three pools, one 20' x 40' in New England, and two much smaller 12' x 18' pools on St. John, in the U.S. Virgin Islands. This post is focused on the two smaller pools. Both homes are short-term rentals, and nearly fully booked year-round. They get weekly service by pool maintenance guys, but I have concluded that their approach to pool chemistry is all wrong. They mostly use tri-chlor tabs, but since there is no winter drain down, the CYA levels are off the charts, which also requires very high FC levels. I recently bought a Taylor K-2006 test kit, but I would have to dilute the pool water to even get a reading on the Taylor test.

It would be nearly $500 per pool to dump the pool water and start over, but I am considering doing this. I like the bleach, baking soda, and borax approach. The only intervals for pool service are weekly, so if the FC levels would drop too far during a week, some automated way to add chlorine would be needed. A mid-week service visit is another option, but that would be pricey. While the pools are small (6500 gallons), it is very sunny, and we use solar pool heaters to keep the water temperature in the low to mid eighties. Electricity is expensive (52 cents a kW-hr), so I use a variable speed Pentair pump set to a fairly low RPM (1500). I have flow meters, and this pump operating from 9:30 AM to 4:30 PM (when the solar heaters receive sun) is enough to move all of the water through the filter once each day. I am aware of SWG's, and while a small one wouldn't use that much electricity, they would lower pH, and appear prone to technical issues that the local pool guy would not be able to diagnose or address.

My questions are as follows:

Would a once a week application of liquid bleach work, or would some more frequent delivery method be necessary?

What daily decline in FC levels should I expect?

Could a once a week application of bleach or liquid chlorine serve as a shock, and still have enough FC level left one week later?

Would an increased level of CYA help in this case? I see recommendations of 40 ppm. What level would work best?

Is there any anti-algal value to adding salt in the absence of an SWG?

Should I hook up a peristaltic pump and add liquid chlorine that way?

Or should I use an SWG and simply plan on regular replacement of the cell before it can decline in effectiveness?

Thanks in advance!

Kevin

[chem geek]

I am aware of SWG's, and while a small one wouldn't use that much electricity, they would lower pH, and appear prone to technical issues that the local pool guy would not be able to diagnose or address. My questions are as follows:Would a once a week application of liquid bleach work, or would some more frequent delivery method be necessary?What daily decline in FC levels should I expect?Could a once a week application of bleach or liquid chlorine serve as a shock, and still have enough FC level left one week later?Would an increased level of CYA help in this case? I see recommendations of 40 ppm. What level would work best?Is there any anti-algal value to adding salt in the absence of an SWG?Should I hook up a peristaltic pump and add liquid chlorine that way?Or should I use an SWG and simply plan on regular replacement of the cell before it can decline in effectiveness?Thanks in advance!Kevin

I believe you meant that SWGs would RAISE pH. They don't lower pH.

As for weekly application of chlorinating liquid or bleach, it is possible but requires rather large swings of chlorine. There are some pool services that do this though some use some chlorine gas as well. They have 100 ppm CYA and increase the FC to around 14 ppm and then this drops to around 4 ppm when they visit the next week. Though this sounds high, 14 ppm FC with 100 ppm CYA is equivalent to 4.3 ppm FC with 30 ppm CYA or 0.14 ppm FC with no CYA so far lower than commercial/public indoor pools that typically do not have any CYA.

You can get a peristaltic pump to deliver chlorine more regularly, but that will have some maintenance issues so might be similar to having an SWG. The pH needs to be maintained in any event, but the pool service should be able to handle at least that.

The other approach that is usually done by most pool services is to use an algaecide or phosphate remover. Polyquat 60 applied weekly will help prevent algae growth even if the FC/CYA ratio gets low due to the climbing CYA level. A phosphate remover can take most of the edge off of algae growth. Other options have more side effects such as copper ions that can stain.

By the way, you should use winter rain (or summer rain if that happens) to dilute the water in the pool and try and keep the CYA at least somewhat in check each year.

[Coconuts]

Chem geek: Thanks. I did know about the pH direction, having done electrolysis before, but screwed up getting it on paper. It seems as though weekly visits would be stretching things as far as discrete bleach addition is concerned. So perhaps either a bleach pump or an SWG makes the most sense. I think that the Pentair IC15 would be big enough given the size of the pools. Are any more concentrated bleaches than 10% available? Who makes a good pump? In sunny climes such as Florida, what is the recommended CYA level? And where does any phosphate come from? Thanks.

Kevin

[chem geek]

The chlorinating liquid I get at my local pool store is 12.5% and some people get 15% but you usually don't find anything higher than that since it degrades faster -- in proportion to the square of the concentration.

I don't know about the brands of peristaltic pumps, but there is also The Liquidator as an option.

For sunny climates such as Florida, you'll need at least 50 ppm CYA. Some people go up as high as 80, but you then need to be very diligent since fighting an algae bloom at that high a CYA level requires a very high chlorine level -- fighting algae needs roughly an FC that is 40% of the CYA level to kill it off reasonably quickly. That's why prevention is much easier.

[Coconuts]

Decision made. It turns out that a supply company on the neighboring island offers free delivery to St. John, and they sell a 55 gallon plastic barrel with 10.5% sodium hypochlorite solution for $210.00. I purchased a Rola Chem RC-25/53 SC, along with a digital timer. The liquid chlorine barrel shows up tomorrow morning, and the pump and timer were installed today. No changes to CYA, calcium, or pH levels, daily chlorination, and the 55 gallon barrel should last for over a year. Assuming that it works well, I will duplicate this at our next door property. The one remaining decision will be to discard the pool water (which has really high CYA levels), and start over. Water is 8-10 cents a gallon here.

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All the best,

Kevin

[chem geek]

Sounds good. Just don't forget to put some CYA in the water initially, either by adding pure CYA or by using Dichlor initially to build up CYA. If there is no CYA in the water, then the chlorine will be too strong and will be harsh on equipment, hot tub covers, swimsuits, skin and hair and will outgas more quickly as well.

[Coconuts]

"Just don't forget to put some CYA in the water" Absolutely; 50 ppm CYA might be about right; perhaps a bit higher due to the strong sun. I just learned that liquid chlorine undergoes self-decomposition, which is a function of temperature and concentration. Stored in the garage at 75F, the 10.5% initial concentration would drop in half over a year. Since I have the second home next door, I will get a second carboy, split the 55 gallons between the two homes, and dilute it down to 5%, which should triple the half life.

All the best,

Kevin

[chem geek]

If you dilute the chlorine, be sure to use very pure water that has no metals in it. Metal ions in the water accelerate the chlorine degradation (for concentrated chlorine -- not noticeable in dilute concentrations as in pools).