Is it possible to go to weekly chlorine additions?

[Steve_in_NC]

Would it be possible to raise CYA to 100 or so and just add all the chlorine needed once weekly? Will that make the chlorine last long enough to go a week?

For example, if using 3ppm per day, could 21ppm be added once weekly?

[PoolDoc]

Yes.

I've described doing that several years back, but it was one of the ideas received poorly by various folk who were here then.

There are some downsides, and it's not for everyone. For example, dealing with algae can difficult, since with CYA = 150, controlling mustard algae can require chlorine levels above 75 ppm!

However, I'd be interested in working directly with you, since I have only limited field data on what sort of problems people might encounter using this approach. To go further, you'll need:

1. A K-2006 test kit and a Hach 562227 Phosphate Test Kit.
2. Complete test results on BOTH your pool water AND the water you fill with
3. If it's well water, we'll need to do some additional tests.
4. A description of your pool (volume, type, filter type + size, pump type + size)
5. Past issues (if any) you've had with maintaining your water. (Various pools, in various locations, some times have recurring problems due fill water, nearby bodies of water, overhanging vegetation, etc.)
6. How YOU use the pool (number of users at one time, frequency, age and water-time duration).
7. How often you have to ADD more water, and how MUCH each time.
8. Information about how much PHYSICAL debris (leaves, dust, etc) your pool accumulates in a week.

The goals would be

1. Lowered chemical costs
2. 1x per week chemical service
3. Algae free operation.

Let me know if you're interested.

[Steve_in_NC]

I'm investigating. At this point, I'm not ready to do it until I understand the concepts.

I assume from your comments that CYA would need to be 150 with very low phosphates. Any other important concepts to the method? I'm considering trying the method in a small pool to see if it works first.

[PoolDoc]

So-called "chlorine shooters" in S. Cali and Arizona have done it for years, but only in concrete pools with deep ends. They'd run CYA between 100 and 150 and inject about 15 - 20 ppm of chlorine, as gas, into the deep end. "Pool Chlor" was one of the biggest of these companies.

Low phosphates is a whole other thing. The way it's marketed mostly does NOT work. If you want to do both, you probably need to learn to do low phosphates, first. Phosphate control is a METHOD, not a CHEMICAL. If you MASTER low phosphates, then you won't necessarily need to go high CYA / high chlorine to enable 1x per week treatment.

Though, what you'd probably need is 1x per week, plus a small standard bleach dose every time the pool was used. For many IG pool owners, that's about 1x per week. But if your pool is used a lot, then the protocol would have to be adjusted.

[Steve_in_NC]

The low phosphate concept is good.

However I looked at some of the products and found that they contain a proprietary mixture of rare earth metals. These compounds precipitate the phosphates which can be cleaned out by filtration. The problem that I have with this is that rare earth metals are often mined together and difficult to separate.

Some of these rare earth metals are radioactive. I'd hate to add something radioactive to my pool.

[PoolDoc]

Not sure that's really the problem with the phosphate removal process. But you know best.

[chem geek]

Welcome back Ben! I only found out today that you are back on the forum.

Regarding phosphate control, I remember that when we talked a while ago you had some commercial/public pools with algae problems, mostly yellow/mustard, and tried using lower phosphate levels to control them and found that effective.

Assuming one used a decent phosphate remover product that worked well, why wouldn't one lower the phosphate level (towards 100 ppb and certainly below 500 ppb) and then target a lower FC/CYA ratio in the 3-4% range instead of the 7.5% of TFP or the 5% you are now quoting? One would save a lot on the chlorine since its loss is related to the FC level all else equal. So that's a lot less to buy and to carry (4 gallons of chlorinating liquid in a crate is nearly 40 pounds). That then opens up being able to use other chlorine sources such as Cal-Hypo and have a slower CH rise from its use.

I agree with you that many phosphate reducers are not good -- they are weak, have extra chemicals (clarifiers, etc.), and are expensive, but two of them don't have these problems. They are very concentrated, are lanthanum chloride in water, have no clarifiers or other chemicals, and are reasonably priced. These are Orenda PR-10,000 and SeaKlear (now Natural Chemistry) Commercial Strength Phosphate Remover. Both reduce roughly 7000-10,000 ppb in 10,000 gallons for one quart and that costs around $30-$35. For many pools, the first treatment costs some (though 1000 ppb reduction in 18,000 gallons would be under $10) but maintenance is very low cost (typically < $5/year). It's taken 5 years for my phosphate levels to rise 500 ppb but I have a pool cover. It's a night and day difference in pool "reactivity" with regard to the rate of algae growth / chlorine demand with higher vs. lower phosphates.

Obviously, pools with metal problems that use HEDP metal sequestrant can't hope to have phosphates be lower so they'd either have to use the traditional higher FC/CYA levels for algae prevention or they'd have to switch to a polymeric or other non-phosphate metal sequestrant (e.g. Orenda SC-1000). And of course with an anionic polymeric metal sequestrant one can't use a cationic polymeric algaecide like Polyquat or else one gets a precipitated mess. On the other hand, even the simpler approach of minimizing the parameters to adjust/treat still has "rules" like never use a clarifier in a pool with a DE filter so at some point you have to know what you are doing. Simpler is not necessarily lowest cost nor least risky ("reactive") if things go wrong.

As for the CYA level not needing to be as high when using phosphates, you can combine the approach of a low FC/CYA ratio with low phosphates and have the CYA level be higher since that reduces loss from sunlight the most. We never figured out the physics/chemistry of what Mark saw with his tests and confirmed in people's pools that showed lower chlorine loss from higher CYA levels even when the FC/CYA ratio was kept constant. There may be some direct CYA shielding effect but I don't have CYA (and CYA-Cl) UV absorption data in the sunlight range though do hope to get that at some point to get to the bottom of this.

Richard

[chem geek]

I just saw this post of yours that answers some of my questions. So we're probably on the same page with regard to phosphate control and you can see if what you've learned with the commercial/public pools can be applied well with residential pools with the caveat that one must do it right (i.e. right product, right treatment method, understanding of restrictions/limitations, etc.).

[Palmyra]

Starting with fresh water, I brought my pool up to about 40ppm CYA for a couple of years. After having read about the potential "shielding" effects, I raised my CYA level to 80-90ppm and did, indeed, see a reduction in loss of chlorine due to sunlight. I realize that can't help much with a shallow pool, but my anecdotal evidence seems to support the notion of shielding chlorine at deeper depths...,.

Thanks for a heads-up on the better options for phosphate removal.

Its great to see your posts again, Richard....