CYA level when running SWG and ORP probe

Costas > DownUnder

Bronze Supporter
Dec 17, 2017
617
Adelaide | Australia
Looking at having a pool installed in early 2018.

I have been reading up on TFP forums as much as possible to gain valuable insight to running a pool (will be 1st time owner)... So far the forums have been a goldmine of information...:thumleft:

One thing that has been a little confusing is the manual for the pool chlorinator that my PB will be installing.

It is a commonly utilised unit here DownUnder - Astral eQuilibrium series chlorinator. eQuilibrium Chlorinator | AstralPool


I was looking at purchasing the version that has the auto acid dosing feature (fitted with PH probe) as well as having a dedicated probe to measure ORP.

In the manual the manufacturer effectively states (prefers) that users should run with no CYA present in the pool.

Reason being is that CYA levels influence the ORP probe's readings, which in turn tricks the chlorinator in producing too much FC.

They do state that if the user does use CYA then levels should be kept at 10 to 20ppm.

Their reasoning is that users should just rely on the SWG to produce enough FC during sunlight hours to counter the UV losses etc and little CYA will not affect the probe's output too much..


If I want to follow the TFP way... then I would obviously like to run CYA up at 70 to 80ppm (pool will be FG) to take advantage of its benefits (lower run time for SWG cell, reduced pump run time and its buffering effect on FC losses etc).

Can I not simply just offset the ORP set point to a lower mV value to allow for the probe's lower reading with a higher CYA level?

The user manual does go some way into explaining this on pg 21 - The manufacturer lists a short table of mV values wrt CYA and FC levels however it pretty much stops at 50ppm CYA levels.

Is there any detrimental effect in running CYA up at around 80ppm with an ORP probe for the chlorinator's chlorine feedback loop (providing I offset the ORP set point correctly)?

I'm not sure how linear the ORP probe's output is so I am not sure whether CYA levels at 80ppm will be workable or not for the ORP probe.
 

Costas > DownUnder

Bronze Supporter
Dec 17, 2017
617
Adelaide | Australia
Hi, we are building Feb 18. Our contract includes an Astral EQ35 salt water chlorinator with ph control (auto acid dosing). Not sure about the cya. Will have to look into our system.
My PB has the EQ35 on my quote - I was thinking that I may move up to the EQ45 which is exactly the same main unit just kitted out with the next size up chlorinator cell.
 

riley00dog

Gold Supporter
Nov 14, 2017
2,213
Brisbane, Qld, Australia
I just read the manual and didn't see mention of cya... it was a quick read though. We're only building a very small pool so I think we will be ok with the 35 but i wouldn't hesitate to upgrade to the 45 if I thought necessary.
 

Costas > DownUnder

Bronze Supporter
Dec 17, 2017
617
Adelaide | Australia

tim5055

Mod Squad
TFP Expert
LifeTime Supporter
May 11, 2014
10,378
Franklin, NC
When dealing with SWCG you need to understand that they have a finite lifespan. If you run it wide open at 100% you end up,with half of the useful life than if you are able to run it at 50%. So, how do we reduce the %?

First, use CYA to protect the chlorine from the UV rays of the sun. It’s easy for the pool builder to,say you don’t need CYA, he doesn’t pay for the replacement cell.

Second, always oversize the salt cell. If you have a 20,000 gallon pool you want a salt cell rated for 40,000 gallons. It cost a little more to oversize the cell, but not double.
 

Jezza

LifeTime Supporter
TFP Guide
Jan 18, 2015
990
Bunbury, WA, Australia
I'd forget the ORP and even the auto acid dosing and just run with the SWG. ORP will generally not work with CYA above 50, which goes against the recommended level of 70-80 CYA for a SWG pool. It's also one less thing to have to muck around with and of course there is the added expense

The beauty of having higher CYA levels is that you will find you lose less FC anyway. Then it's just a matter of fine tuning your SWG to maintain the correct FC levels. As Tim pointed out it's more important to get a SWG rated at least twice the size for your sized pool and that would be where I would be putting the dollars saved from not buying the ORP.

At the end of the day you can't 'automate' a good testing regime with one of the recommended testing kits.
 

riley00dog

Gold Supporter
Nov 14, 2017
2,213
Brisbane, Qld, Australia
I've figured out the confusion. Your link to the eq35 is for the eQuilibirum as per your link. My model is also an eq35 but a different series. I can see where yours warns against cya. Mine is the eq35 from the e series rather then the eQuilibrium series. No warnings at all re cya. My pool builder has already given me a ton of information on the importance of the cya/fc relationship, so thought it was weird that he would install a chlorinator that warns against cya. Here's the link to mine. E Series Salt Chlorinator | AstralPool
 

Costas > DownUnder

Bronze Supporter
Dec 17, 2017
617
Adelaide | Australia
ORP will generally not work with CYA above 50,
That is what I wanted confirmation of - Thanks

The acid dosing feature is fairly basic so I thought that shouldn't cause too much drama from an automation perspective (PH sensor working in conjunction with peristaltic pump).

I will also be up-sizing the SWG cell to take advantage of those benefits.

I will also be purchasing a comprehensive testing kit (Clear Choice Labs kit) when it is time to fill the pool...:)



Mine is the eq35 from the e series rather then the eQuilibrium series. No warnings at all re cya.
That model relies on a timer system to control the on/off periods for the SWG whereas the model I linked to uses timers but can also use an ORP probe to allow it to control the output from the SWG cell.
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
15,864
Tucson, AZ
If you want an acid dosing system, then just get one that runs on a duty-cycle based method without any closed-loop feedback from a probe. Probes add a complexity to the management process of a pool that is really unwarranted in most residential situations. There is no need to control pH to any absolute value - a pool is perfectly swimmable with a pH anywhere between 7.2 and 8.0. Anyone that tells you it has to be an exact value, like 7.4 which everyone quotes as being suitable for the human body, simply does not understand the chemistry involved.

A simplified acid dosing system used in conjunction with reagent based testing will be more than sufficient to keep your pool clean and healthy to swim in.

- - - Updated - - -

Oh, and you really want CYA in your pool water. While it is true that cyanuric acid protects chlorine from excessive UV photolysis, it also has a much more important benefit - active chlorine buffering. CYA acts as a chlorine buffer (holds chlorine in reserve) and reduces the levels of active chlorine in water to ppb levels. This is VERY important for both bather comfort as well as the formation of disinfection by-products (DBPs). 1ppm FC with zero CYA in the water has almost 5X the active chlorine levels (hypochlorous acid) as water with 3.75ppm FC and 50ppm CYA. The difference in bather comfort is very profound which is why people who use public pools a lot (public pools typically are barred from using CYA) find that their hair is dry, their eyes sting and their swim clothes don't last very long.
 

Costas > DownUnder

Bronze Supporter
Dec 17, 2017
617
Adelaide | Australia
Oh, and you really want CYA in your pool water. While it is true that cyanuric acid protects chlorine from excessive UV photolysis, it also has a much more important benefit - active chlorine buffering. CYA acts as a chlorine buffer
Yes - I had read this very important benefit in a much older post on the forum when I was researching CYA levels on the forum.

This is what triggered my original question in regards to the CYA levels Vs ORP probe measurement values etc.

Thanks for the tips....
 

AUSpool

Bronze Supporter
LifeTime Supporter
TFP Guide
Sep 23, 2015
667
Brisbane, Australia.
I personally think that a pH probe and to a greater extent, the ORP probe are an absolute waste of time and money, you’ll end up chasing numbers that may or may not have any relevance to what’s actually happening in your pool. Probes have a short life span and must be regularly re-calibrated.

Look at importing a decent test kit, the Taylor K-2006 with FAS-DPD chlorine test or tests kits from Clear Choice Labs https://clearchoicelabs.com.au/, test your actual FC level and adjust the SWG as needed - simple.

In Adelaide I would expect your TA to slowly climb due to evaporation with low rainfall. I maintain two pools, one with BA and one without, both have a stable pH at 7.8 so I leave them at 7.8. The TA in both slowly increases and I reduce it as needed with acid - I’m effectively using acid to manage my TA and not needed to manage pH.
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
15,864
Tucson, AZ
.... you’ll end up chasing numbers that may or may not have any relevance to what’s actually happening in your pool....
+1

This is the problem with ORP - there are studies and data that show water with an ORP at 650mV (considered "sanitizing" by CDC standards) that have little correlation to the exact active chlorine (hypochlorous) concentration in the water sample. So what this means is that in practice you need to not only be able to get your ORP probe to register and maintain a voltage at the correct "sanitizing" level BUT also ensure that the ORP voltage correlates to an appropriate FC/CYA ratio. There are many factors that can influence the ORP reading and so one has to carefully study what their pool is doing OR simply setup the system and "hope" an algae bloom doesn't occur or no one gets sick. And, once that correlation is known, it has to be tracked over time as changes in the water chemistry can cause drift.

I would say it's A LOT easier to simply use a good test kit to measure your water on regular basis and correct the chemistry as needed than "hope & pray" the probes are working right. With an SWG pool, once you get the FC level dialed in for the specific pump runtimes you use, the FC levels drift very slowly and predictably. Initially one will do a lot of testing to learn how their water behaves but, once that initial break-in period is done, a seasoned pool tester can practically guess what their water chemistry levels are and be within 10-20% of the right answer.
 

Costas > DownUnder

Bronze Supporter
Dec 17, 2017
617
Adelaide | Australia
I personally think that a pH probe and to a greater extent, the ORP probe are an absolute waste of time and money, you’ll end up chasing numbers that may or may not have any relevance to what’s actually happening in your pool.
+1

This is the problem with ORP - there are studies and data that show water with an ORP at 650mV (considered "sanitizing" by CDC standards) that have little correlation to the exact active chlorine (hypochlorous) concentration in the water sample. So what this means is that in practice you need to not only be able to get your ORP probe to register and maintain a voltage at the correct "sanitizing" level BUT also ensure that the ORP voltage correlates to an appropriate FC/CYA ratio.

Thanks for confirming this.

It did pass my mind that I could end up simply 'chasing my tail' so to speak if I was relying on probes etc for feedback

When it comes time, I will be ordering a decent test kit (Clear Choice Labs - Easier to source here DownUnder than the Taylors kit) and rely on this for my feedback mechanism to manage the water quality.

I will also be up sizing the SWG as recommended.

I have my PB coming around next week for a detailed measure & quote (Final?) of the grounds etc So I will scope out the equipment choice before then and select accordingly.

Thanks
 

AusJohn

Active member
I've been looking at one of these units too, unlike you I have a newly relined concrete pool. From what I understand the unit can operate with an acid feeder configured without a pH probe, that can simply be tuned to dose your regular acid dose if one is required. With the new lining on the concrete pool which causes quite a high acid demand over the course of some months I have opted to go with a pH probe as I travel a lot and the unit can maintain a sensible pH while I'm away and my wife doesn't have to mess around handling acid regularly. Once the liner is fully cured, I will probably decommission the pH probe as it won't really be required. As you have already learned here, the ORP probes are problematic in terms of getting consistent results when the pool is stabilised, an ORP probe generally costs in the region of five hundred bucks (AUD) and can last as little as a year, so they're also an expensive option and require regular cleaning and maintenance. With a fibreglass pool, I would probably go without the pH probe unless you are away from home too much to keep proper tabs on the pH levels to adjust the feeder to the required level. You will also notice that the manual recommends cleaning the pH probe with JIFF, an abrasive household cleaner. If you do get a pH probe, I would highly recommend disregarding this as a short soak in dilute detergent will generally do the job quite well where the abrasive cleaner will quite quickly destroy the extremely delicate glass membrane of the probe. I may be cynical but those cleaning instructions will result in them selling a lot more probes.
 

needsajet

TFP Expert
LifeTime Supporter
Jan 4, 2016
4,692
Sydney, NSW, Australia
Welcome to TFP! Good to have you here :)

This thread is helpful We don't recommend ORP. Unfortunately it's not just an offset for CYA; the challenges associated with using ORP as a proxy for FC are much broader.

I do three pools and weekly pH adjustment has been fine. I tried an acid doser, but it was the same amount of work in the end. Depending on the test result and size of pool, I add 150 to 400 ml of hydrochloric acid once weekly and it gets the job done for very little effort. That spreads out gradually to about once a month in winter. I've seen a few threads where people set acid dosing unnecessarily low (e.g. pH 7.5) and consumed more acid and ended up also having to add bicarb (Alkalinity Up) which wouldn't have been necessary had they left the pH up around 7.8.

I started out thinking chem automation made a lot of sense, and really had to convince myself not to go that route. Overall, I'm thankful to have bumped into TFP at the right time!
 

AusJohn

Active member
So I got a quote back for the Equilibrium unit and it's not exactly cheap. The documentation doesn't list any specs on the pH measurement system although you can see from the pics in the manual that the resolution is 0.1 pH unit. I've had a look at most of the other options around using pH probes from pool equipment manufacturers and my conclusion is that they all appear to be using the cheapest nastiest probes and electronics that they can get away with. Reading the manuals it appears that they know nothing about pH measurement or care of probes. The price I was quoted for the Equilibrium probe, I could by three good quality industrial probes.

I have enquired after the specs from Astral but two days later have heard nothing back from them. Assuming similar specs to the other manufacturers I'd say the systems are essentially decorative and I wouldn't trust the readings that they're getting. I am going to install a system, but it will be configured based on and industrial pH controller with resolution and accuracy levels that are an order of magnitude better. I reckon it will end up being cheaper than the Equilibrium system by a substantial margin. The industrial controller will need a cabinet or enclosure a decent quality probe and a separate dosing pump. Just going to go with a direct replacement of my simple SWG at a quarter of the price of the Astral unit which leaves me plenty of leeway to install separate pH control.

I did find one unit set up for pools that had decent specs, it was from Hanna Instruments, who do decent lab and industrial gear, not high end stuff but it's OK. The reason I didn't go for it is that it's set up as a liquid chlorine dosing system as well as a pH controller so not really suitable for a stabilised outdoor pool. It was also using a fairly pricey ($400) combined pH and ORP sensor so that pushes up the maintenance cost too. I'm currently looking at one of their small industrial controllers instead. I'll update as I progress.