CYA-chlorine review

[jvf]

Hello,
I have been studying the CYA-chlorine relationship chart provided by Chem Geek et al. This is a well thought out analysis and the chemistry seems correct. But, no surprise, it brings into question recommended industry standards (at least in my case). We have a small (2400gal) outdoor vinyl exercise pool. Recommended FC levels by the manuf. Are .5 to 1.5ppm. and CYA 20-50. Possibly they are at the lower level because of perceived vinyl liner problems if chlorine levels are too high. An article on vinyl basics in Pool and Spa News lists 1-4 ppm as a guideline. This at least puts Chem Geek’s suggested level of 4-6 ppm with CYA of 30 almost within reason (my CYA is 35).

But, on the face of it, the charts also seem to go against other opinions given here that the goal is to keep chlorine levels as low as possible but still be effective. Nice to say but, other than no one getting sick, how to measure effectiveness? ORP readings, which I’ve made, are not well thought of here by many (perhaps because they’re difficult to make) but were a main measurement of a water filtration company I worked for that sold commercial fish tanks.

When I started taking care of the pool CYA was 20 and I later bumped it up to stabilize things during the day when the cover was open. I also see that CYA of 20 is not recommended per the chart. But, all things being equal (Ph, temp, etc.) ORP is also affected by CYA being lower as CYA goes up. I’m thinking that after our next water change I’m going to keep CYA around 10 or 20 and monitor chlorine more frequently keeping it at the 1-1.5 ppm level.

What levels of chlorine do those of you with vinyl pools strive to maintain?

Thanks,
jvf

 

[Donldson]

I use the levels found in the [FC/CYA][/FC/CYA]

Why would I give industry standards, which at this time treat FC and CYA as complete unrelated and uncomplimentary values, any thought at all when it has proven to be nothing but a boilerplate number that hasn't been meaningfully updated in my lifetime?

Except in instances of public pools the standards can (and should) be ignored without consequence.

 

[jvf]

Yes,
That’s the chart I’m referring to. I don’t trust industry boilerplate “standards” either which is why I continue to search out information.

 

[Jimrahbe]

jvf,

So what is this great "fear" you seem to have of chlorine? Obviously, it is your pool and you can do whatever you want, but I can't understand why you would want to run your FC so low.

What are you trying to prove or avoid?

With a CYA of 20 (which we do not recommend) your FC should be about 4 ppm...

We recommend a minimum CYA of 30 with an FC of about 5 ppm.

Maybe I just don't understand the point of your post...

Thanks,

Jim R.

 

[duraleigh]

I’m going to keep CYA around 10 or 20 and monitor chlorine more frequently keeping it at the 1-1.5 ppm level.

With what do you test? You will have a difficult, if not impossible, task trying to stay in that range.

That sounds like a nice idea but you will have to use a new way of testing that TFP is not aware of.

Additionally, since most pools lose about 2-3 ppm daily (possibly more if you get your CYA down as low as you will attempt, you must come up with a method to apply chlorine 3-4 times daily and then you must test the FC the same number of times.

In short, those numbers won't work.

 

[jvf]

Well,
Since I have no practical experience or preconceptions, I have no fear of any chlorine level per se. But, as I learn how to take care of this machine, I’m trying to practice the “do no harm” portion of the Hippocratic Oath. Those who should know better than I express concern about elevated chlorine levels damaging vinyl liners and I’m trying to avoid doing damage to the liner. It is a relatively new one (18 mos.) and is definitely bleached from the water level down. Above is bright blue and below is light blue.

However, I could ascribe this condition to my hapless bro-in-law who owns the pool. His version of sanitizing was to put a floater in the pool and keep filling it with trichlor tabs. This went on for several months. The first measurements I took revealed that chlorine levels were at shock levels. If this went on for a few months I suppose this could have caused the color change. I tossed the floater in the weeds, pronounced it verboten and proceeded to use liquid chlorine. After chlorine levels got reasonable I got Ph, Alk and the rest into the manuf. recommended values which, apart from chlorine, seem to be in line with conventional thinking.

At the end of the day it’s not about chlorine, it’s about the ability of the system to deal with pathogens, organic matter, etc. Thus ORP, being an indicator of the systems ability to handle said items, might be considered the final arbiter. Too bad it’s such a hard parameter to measure. So, it seems the practical alternative is to keep chlorine levels to some “accepted” level while, in my case, avoiding damage to the pool.

 

[needsajet]

OP asked about issues with vinyl, due to the conflicting recommendations he's seen. A fair question. Welcome to the forum jvf! Good to have you here

The CYA (aka stabilizer, aka cyanuric acid) lessens the 'harshness' of chlorine, and you will not experience any vinyl issues when using the [FC/CYA][/FC/CYA].

For example, at pH 7.6, CYA at 60 ppm, and FC at 6 ppm, only around 0.1 ppm FC is active chlorine (the part which does the sanitizing). If there was no CYA and 1 ppm FC, that figure is 1 ppm active (so-called 'harsh') chlorine. The CYA binds with the free chlorine, holding it as a reserve and rendering around 95% of it as inactive. The constituent that does most of the sanitizing (HOCl, aka hypochlorous acid) is about 0.04 ppm in the stabilized pool, vs. 0.4 in the unstabilized pool (10 times stronger).

The pool industry has been very slow (perhaps intentional) to recognize this relationship, maybe because sales revenue for chemical companies could be reduced, or perhaps it seems complicated to customers. TFPC cuts through it all and presents methods that are safe, reliable, cost effective, and backed by proper science.

You mentioned goals expressed here to keep chlorine levels as low as possible, and I just want to explain TFPC does not include a goal to keep chlorine levels as low as possible, but rather to maintain safe chlorine levels, commensurate with the CYA level. Some posters here like to keep levels near the minimums, perhaps to save money, or because they like it better that way. We also provide safe minimums for FC, generally 7.5% of CYA for liquid chlorinated pools and 4.5% for salt water chlorinated pools. It's safe to swim (and for your liner) up to 40% of CYA, but TFPers only use that level for eliminating algae blooms. I personally like around 10% for day-to-day use, which provides a buffer with young grandchildren in the pool, so I keep my pool around 70-80 ppm CYA and 5-10 ppm FC.

I don't know much about ORP except that sensors can be fouled by CYA.

Have fun with your pool!

 

[woodyp]

I'd be more concerned about the "hapless BIL" management of ph over that length of time. Floaters with pucks will drop it down. Chlorine is not your worst enemy for a vinyl liner OR plaster pool.

 

[jvf]

Thanks everyone, especially to needsajet for giving a good explanation of how chlorine might affect vinyl liners. I was also wandering about a “rule of thumb” for the amount of chlorine that might be lost per day which was also mentioned in the replies. My losses are slightly lower but the pool is covered and not being used now (water is way too cold so we’re looking into solar heating). With my CYA level in mind, I’m going to start out trying to maintain a 3-4 ppm chlorine level.

One great thing about this pool is the swim current propeller. It’s like having a giant egg beater in a bowl. So, rather than worrying about “broadcasting evenly” or “pouring in the four corners of the pool” I just turn on the propeller, pour whatever into the current and let ‘er rip for a few minutes.

 

[needsajet]

During swim season, 2 to 4 ppm FC per day is common. Water under 60 degrees F, and no swimming, you could see 0 to 0.5

It's highly variable from one pool to another, and tends to be higher in smaller pools and lower in larger pools, along with other factors such as hours of sunlight, contamination, number of swimmers, pets swimming, etc.

Adding a signature with your pool information is really helpful. Click the link in my signature to find tips for getting the most from the forum. (New Member Tips)