One more off-topic post and then we better stop! I generally like my water at a refreshing 90 degrees....

Is the SWG FC levels lower than other methods due to the contstant sanitation, or due to the superchlorinating effect as the water passes by?

yes

The lower recommended FC levels when using a SWG have been discovered empirically. They have been observed to work. We are not sure why they work. The two points you made, uniform levels and super chlorination inside the cell, are the two leading theories, but there is no confirmation.

I discovered something over the weekend that reminded me of discussion we used to have concerning chemical companies claims that CYA doesn't matter.

I recently bought a new HTH (Arch Chemicals) test kit at Walmart to get me through the season, and printed in their description of CYA, the state at higher levels it can cause algae and chlorine in-effectiveness and below the low range inefficient use of chlorine. They recommend a range of 30-50ppm. I just found this page on their website-

http://www.archchemicals.com/Fed/HTH/Po ... zation.htm

Of course, they claim "HTH® and calcium hypochlorite (cal hypo) offer the only complete solution to overstabilization. Cal hypo products do not contain cyanuric acid and will not cause overstabilization." No mention of the problems Cal Hypo can cause

I also noticed they are now selling HTH liquid chlorine, ie 10% SH at Walmart, $12 for 2-1gal jugs. No mention of it as an option in their right up, mark up must not be as profitable for them

Also on their website about stabilization-

http://www.archchemicals.com/Fed/HTH/Po ... ancing.htm

"The cyanuric acid level and the climate determine whether you need to stabilize your pool. You can use an HTH® Test Kit to determine the cyanuric acid level.
• When opening your pool, the cyanuric acid level should be 20 - 50 ppm. This level means your
water is stabilized.
• During the swimming season, the ideal cyanuric acid level is 20 - 25 ppm. Chlorine isn’t as
effective if the cyanuric acid level gets above 100 ppm."

Interesting

I have an older kit of theirs at home, I plan to see if this disclaimer has always been their or if this is a recent development. Edit- I checked. It was in their kit last year as well.

Yes, there are a relatively small number of manufacturers of various pool and spa chemical products and I list some of them in this post. Chemtura focuses on stabilized chlorine and does not make any Cal-Hypo. Arch Chemicals historically focused only on Cal-Hypo, but later on also offered stabilized chlorine and now apparently offers chlorinating liquid as well. So yes, each company makes their own claims, points out the negative attributes of competitor's products and leaves out the negative part about their own products (i.e. they intentionally withhold materially important information a consumer would need to know to make an informed purchase decision). The "overstabilization" issue is a controversy as far as these companies are concerned, but for all of us with real pools that demonstrate the reality of the chlorine/CYA relationship, there is no controversy.

Chemtura does not deny the chemistry described in the 1974 O'Brien paper, but they do say that they don't believe it occurs or applies to "real pools". I don't believe they are claiming that real pools are a parallel or alternative universe, but that there are so many other things that happen in real pools that can slow down chlorine kill times. Of course, this is true, but irrelevant, much like a typical lawyer argument (i.e. truthful but misleading). In real pools, one has bacteria in clumps and biofilms, pathogens encased in droplets of mucous or fecal matter, lots of other chemicals in the water some of which may interfere with chlorine effectiveness, etc. Though this is all true, all of these factors simply make matters worse in terms of chlorine net effectiveness -- they don't change the fact that most of the chlorine is bound to CYA. In high-bather load pools, one may have an additional effect since there may be so much sweat/urine that there is substantial monochloramine that is formed (which shows up as Combined Chlorine). This can then lead to faster kill times in spite of high CYA levels since monochloramine doesn't bind to CYA (in fact, this is the basis of ammonium sulfate algaecides). However, most residential pools don't have these effects so the chlorine/CYA relationship becomes the dominant factor in determining whether chlorine alone can prevent algae growth when conditions for such growth are favorable (i.e. sufficient algal nutrients, sunlight, etc.).

Richard

I had a strange conversation with a pool store employee about CYA and the amount of chlorine required. I went in to purchase liquid chlorine and get some stabilizer (my CYA was below 30). So They guys recommends I get Trichlor, which is fine for a quick fix, but then he proceeds to tell me I dont need liquid chlorine and to just use trichlor all the time. I say whoooo, I don't was to elevate my CYA levels. He says it doesn't matter, and rambles on how he is a certified pool tech and just finished his course. He then proceeds to mention something about the EPA on requires 2 ppm of chlorine and something about more is dangerous. I told him it all depends on the amount of CYA; the more CYA the more chlorine you will need to achieve your minimum FC level to protect against algae. He starts talking about cryptosporidium and I just stopped him and said, "the customer is always right, so just tell me I'm right and I'll continue to come here. Otherwise, I'm gone." I just didn't want to listen to his **** anymore. He apologizes. So I tell him to check out TFP and see the real scoop on chlorine/CYA.

I can only imagine what they teach in the "certification" courses. Strange how he didn't know there is a relationship between CYA and chlorine levels.

They do not teach the chlorine / CYA relationship in the NSPF CPO nor the APSP TECH courses nor any other courses that I am aware of. I'm trying to get that changed, starting with the NSPF CPO course and I've written about that in this thread where that's just one of several topics missing or incorrect in the course (or at least the CPO Handbook since I have that, but have not taken the course). I've given my feedback to NSPF (including extensive comments and new tables and new or changed text) and we'll see if anything changes.

Me, too.

In the course of some web surfing I stumbled across the LA County Health Dept section on pools. Pool Boys have to be certified to open a business! But I wonder how many even pay attention to this chart?

In another section, dealing with accidents, they posted this rule:You ain't gonna stay below 50 ppm for long on a steady diet of pucks!

I've read this entire thread, and I have a question that seems to fit. Why would someone bother trying to maintain FC levels down at 2-3ppm which is relatively low and more prone to allow algae to develop? It would take frequent checking/maintaining of the level to make certain it didn't go any lower. Why not just maintain at a higher ppm? Say 6 or 8ppm and then forget about it?

I have a SWG and typically maintain a 70-80ppm CYA level. My FC min/target is about 4/6ppm. Last year (when I first bought the new house/pool), I know my FC was higher than 5ppm all summer b/c it was always over-range on my test kit. In hindsight, I know I ran my SWG more than necessary, but at the same time, the pool was crystal clear and perfect the entire time. This year, I've got my new TF-100 kit and am taking things more seriously. I can now use FAS-DPD to measure FC more accurately. It was 9.0 when I first started testing a couple of weeks ago. I've dialed my cell back and the FC is now 6.0, and I intend to target 6.0 this summer.

But my question remains -- why not just target 8-10ppm and be done with it? (assuming one isn't worried about the extra cost of higher cell output and/or longer pump run time)

Thanks.

Nearly everyone is worried about the extra costs. Running the FC level a little high is fine, it just wastes money.

I'm not so sure about that regarding the costs. Those costs aren't like going to the pool store and buying chems and incuring an immediate expense. These are very indirect/hard-to-quantify costs. A little extra electricity for the pump, a little shorter life for the salt cell. Coupling the indirect nature of those expenses with the strong desire to avoid algae and keep the pool maintenance easy, it seems like alot of people would want to avoid targeting low, borderline FC levels.

Every pool is different, so our recommendations are not perfect for everyone, but it was our intention to recommend levels that work for just about everyone and are trouble free. I wouldn't call them "borderline" in any sense.

The cell in a SWG will produce a fixed amount of chlorine in it's lifetime. If you run at a higher FC level it will shorten the cell life in a very predictable way. Replacing the cell in a SWG can be fairly expensive, and in the long run ends up costing just about the same as it would have cost to add chlorine manually. So there is nothing "hard-to-quantify" about it.

If you want to spend the money to get some peace of mind, then fine. But most people are interested in reducing costs, so much so that it is one of the fundamental goals of our system of pool care.

Also, maintaining a higher FC in an SWG pool means more chlorine loss so a longer SWG on-time. That often leads to a faster rise in pH so more acid needed to compensate for pH. The extra cost isn't just in the SWG on-time electricity and shortened cell life, but also in the acid and inconvenience in the possibly greater frequency of pH adjustment.

Now that's an interesting point, running a higher FC level means wearing out the cell and a higher chlorine loss, why?
If there is nothing in the pool consuming the chlorine, then the only extra chlorine is that boost from say 2ppm to 6ppm once at that target the actual chlorine loss say 1ppm/day should be the same.

At the same CYA level, a higher FC level results in greater loss of chlorine from breakdown by the UV in sunlight. Also, the active chlorine (hypochlorous acid) concentration is higher so any reactions it is participating in for which it is a rate-limiting step would go faster, including oxidation of miscellaneous materials in the pool (not just algae, but pool surfaces including covers and even oxidizing CYA itself). The former effect is the dominant one so if one has an indoor pool or a pool that is covered most of the time (with a mostly opaque cover), then there won't be much difference in a higher FC level, though the absolute FC loss will be low anyway so the SWG on-time will already be low in this case.

Quite so Richard, I posted that rather badly. It was PhillipH's figs I was considering with his CYA level and then just added my 2-6ppm example without thinking it through, sorry.

Phillip,

Just remember that the FC number by itself is almost meaningless. It only tells you the chlorine capacity so that you don't run out. It doesn't tell you strength of the chlorine in terms of sanitation or oxidation. That is more related to the FC/CYA ratio (when CYA is present). So even 2 ppm FC with no CYA is actually quite high while 4 ppm FC with 100 ppm CYA is low and algae can grow.

Richard

Great point. Thank you for clarifying. I should have been more specific and said that I prefer to target my "TargetFC" instead of my "MinFC" based on my specific CYA (target 70-80), but you inferred correctly that I didn't really factor this in when talking about 1-2ppm FC being low.

Thanks for all of your (plural) help on the forum. Probably the best and most helpful forum I've ever come across. It's so important b/c residential pool management can be intimidating and people need answers. You guys provide an excellent resource.