Anyone use an automatic chemical feeder?

[Drew80]

I have a Hayward system with a SWG, and I'm considering adding the Sense and Dispense system to monitor pH and ORP. It's about $1k plus the cost of a CO2 tank, so it's not a trivial purchase.

Anyone have one of these and had good luck with them? Is it worth the price?

 

[mknauss]

Be aware that ORP does not work in outdoor pools. ORP must have very low CYA levels in the pool water for their operation. Even with that, they have maintenance and longevity issues. The pH probes on the units have less problems but still must have regular intervention and calibration.

Also be aware that CO2 does not reduce TA in your water like muriatic acid does. So if your fill water adds significant TA to your pool you will still need MA.

 

[Drew80]

So that's a no then =)

 

[Sark]

Be aware that ORP does not work in outdoor pools. ORP must have very low CYA levels in the pool water for their operation.

Sorry to butt in but this is not true. A truer statement would be CYA levels affect ORP readings. But not in the sense that would lead one to state that they cause them not to work. And they most definitely work on outdoor pools. Not all outdoor pools use cya.

Orp is simply measuring oxidizing potential. What happens when you add cya? Your oxidizing potential goes down. So a quick example of this would be this:

Let's say in your pool an orp reading of 750 correlates to a fc reading of 3.0.
Now let's say you add some cya. The addition of that cya just lowered your oxidizing potential. You are still going to have a 3.0 fc level, but now your sensor might read an orp level in the low 700s.

When it comes to automation feeders (automation feeders and ORP sensors are a county requirement for commercial operations here) your lovely ORP setpoint of 750 that was keeping you a perfect 3.0 fc will now be giving you a much higher fc when the cya is in the pool. This is simply because the oxidizing potential of 3ppm fc is much less now. Your system is going to still aim for that 750 orp that you set it at, it will just require a higher fc level to reach that.

I only bring this up because there is an obvious solution to this. Lower your orp setpoint.
Like I said, we are required to have automatic feeders, and orp sensors. However, the health department doesnt give a darn what the orp level is, they only care about the fc level. So in the summer when we add a bit of cynaric acid (we only use cya in the summer, winter time there is no need and yes our pools are open all year) all we do is lower our orp setpoint until its giving us a fc reading of 3.0, our counties required fc level.
The difference between summer and winter (cya and no cya) is something along the lines of 720 orp in the summer and 770 orp in the winter. Both of those numbers in 1 of our pools give us 3.0ppm fc. the difference is the cya lowering the oxidizing potential and needing to adjust our setpoints.

-Brandon

 

[mknauss]

You are speaking of commercial pools.

This forum is designed for the residential pool owner.

 

[Flying Tivo]

CYA does not disappear in the winter, it is still there and it will accumulate over time, so your set point will always be changing which defeats the automation portion of the process. You still have to be calibrating your readings depending on FC. Even if you have the ORP for regulation purposes you can have an automatic stenner feeder and will do the same job, if not even better stable numbers and less expense in FC due to less burnoff if you have the proper CYA/FC levels.

Felipe

 

[Sark]

0

You are speaking of commercial pools.

This forum is designed for the residential pool owner.

All due respect, orp doesnt care if its measuring a commercial pool or a residential pool. You stated orp sensors dont work when cya is present in the water, and that is incorrect.

-Brandon

 

[Sark]

CYA does not disappear in the winter, it is still there and it will accumulate over time, so your set point will always be changing which defeats the automation portion of the process.

Felipe

I am very much aware of this. But with water changes and back washing throughout the summer. By winter time I get our cya levels back to 0. We only run up to 30 ppm in the summer, which isnt hard to get rid of with the methods I stated. We've been doing it this way for 7 years now and trust me, I adjust the setpoints twice a year. They dont need constant adjusting. And the orp sensors definitely continue to work with cya in the water.

-Brandon

 

[Flying Tivo]

Dont want to get into an argument since your system is working, but since you mention backwashes and water exchanges then your CYA levels are not constant which means your ORP readings are not constant. If you only set your points twice a year your FC levels will not be constant either, they will probably be higher, which is a good thing in commercial pools.

Felipe

 

[JoyfulNoise]

I would avoid ORP based dispensing systems for an outdoor residential pool - the complications in getting them to work correctly far outweighs the benefits they confer. A simple duty cycle driven SWG or Stenner pump will have no problems keeping a pool at appropriate levels with only a few tweaks needed during the year.

Yes, ORP does work on any pool, but the question is how well? Since most residential pool owners need CYA in the water to buffer the chlorine strength and reduce UV photolysis and since SWG pools work better when the CYA is higher (TFP recommended levels for an SWG pool is to have the CYA between 70-90ppm), ORP signal-to-noise ratios drop dramatically making the readings and control point very unstable. ORP is not just sensitive to oxidizer levels but will be affected by all water chemistry parameters. Some of those parameters change slowly over time (pH, TA, etc) but all parameters will affect ORP. So, at the end of the day, you have a probe that is susceptible to a lot of drift and noise unless you operate a pool with little or no CYA making the water very harsh on bathers.

Do you really want to deal with that hassle?

And yes, commercial pools use ORP for control but it is a very telling fact that health departments don’t rely on them but rather require operators to simply track FC (and in many cases, total chlorine). So, if local Health Departments don’t consider them a reliable tool for reporting sanitizer levels, why bother?

As for CO2 being used as pH control, that’s a fine option but a bit much in my opinion unless you’ve got a cheap supplier of gas tanks in your area (check welding shops and paintball suppliers). Muriatic acid is cheaper and can be automated with a simple Stenner pump setup or you can get a retail system.

Your money is better spent elsewhere....

 

[Sark]

Dont want to get into an argument since your system is working, but since you mention backwashes and water exchanges then your CYA levels are not constant which means your ORP readings are not constant. If you only set your points twice a year your FC levels will not be constant either, they will probably be higher, which is a good thing in commercial pools.

Felipe

No argument
I think you are assuming though that we add cya at the beginning of summer and that's it. It gets maintained at 30 ppm the whole summer via weekly cya testing. So there is no constant adjusting of the setpoint. Just occasional additions of cya as needed.

-Brandon

 

[Sark]

And yes, other factors in the water have an affect on orp. pH being the biggest one but th and others having a much smaller affect. But that's still relating back to oxidizing potential. What happens to chlorine when your pool water is at a 8.0 pH? It does basically nothing. Cl in a pool with a pH at 7.2? Much more effective. It's because the chlorine has a higher oxidizing potential at lower pool water pHs.

Anyways, I didnt want to get into a discussion on whether or not orp sensors are viable residentially, I just wanted to point out that the original statement was false, or misleading at best.

-Brandon

 

[JoyfulNoise]

What happens to chlorine when your pool water is at a 8.0 pH? It does basically nothing. Cl in a pool with a pH at 7.2? Much more effective. It's because the chlorine has a higher oxidizing potential at lower pool water pHs.

-Brandon

I think you should read (or re-read) these threads as the above assertion you make is equally as false as saying ORP doesn't work in outdoor pools -

Pool Water Chemistry

Certified Pool Operator (CPO) training -- What is not taught

This is a link to charts which show the standard CPO chart of HOCl/OCl- versus pH (which does not apply to swimming pools at when when CYA is present) and what happens to the HOCl/OCl when CYA is present. As you can see, in all cases, even up to a pH of 8.4, there is sufficient amounts of HOCl to keep the pool water sanitary. The notion that pH creates problems with chlorine is a falsehood that is used over and over again by the pool industry to scare pool owners into using all sorts of chemicals that they don't need and keeping pH levels and alkalinity levels at ranges that are impossible to manage.

HOCl-OCl-noCYA.gif

HOCl-OCl-30CYA.gif

 

[Sark]

Ok fair enough, semantics, it's not useless but it is reduced in effectiveness no doubt. Sufficient =/= ideal. As am sure you'd agree with what's been happening in my last thread with our method of chlorinating. We are sufficient, but not ideal. but even in the last forum thread link you posted it states that even with cya present, hocl will still drop just not as much as it will with no cya added.
So clearly, as I've witnessed for the last 7 years, when you add acid to the pool, the orp level rises. It's not rising because magically more fc is being added. Its raising because its noticing an increase in oxidizing potential.... from the lower pH.

Unless you are trying to tell me pH has no effect on how much hocl is present vs ocl-.... it will definitely affect orp level. Although I will admit we dont use cya for most of the year, and at a lower dosage than seems to be recommended here, so the changes in orp that I see might be more pronounced than in other bodies of water but I can promise you that lowering your pH has an instantaneous affect on your orp reading.
I can record it happening for you too if you want.
Unless I'm misunderstanding the point you were trying to make. maybe my wording of "worthless" was not proper and in should have said less effective.

-Brandon

 

[Flying Tivo]

So clearly, as I've witnessed for the last 7 years, when you add acid to the pool, the orp level rises. It's not rising because magically more fc is being added. Its raising because its noticing an increase in oxidizing potential.... from the lower pH.
-Brandon

This is probably where you have been lead to believe that the FC is more oxidizing, but what its really happening is the ORP is seeing more Noise due to lower pH.

Again your pool your rules!

Felipe