Automatic ORP using Liquid Chlorine and CO2

[dmccarthy]

I recently purchased a Hayward CAT-4000 ORP/PH controller for my commercial, 24,000 gallon indoor pool. I will be installing in the next few weeks once the electrician wires a GFCI outlet and I am going to be using a 15 gallon stenner pump for the chlorine and I have secured a local gas company that is going to lease my out a CO2 bottle to control the pH. Since I am new to this arrangement as I have been using an off-line brominator for years (and have had to deal with all of the issues associated with it) I have been researching whether we are allowed to use CYA in the water or not and I have found nothing (other than all of the information that I have seen in some of the threads over the years) and so I am planning on using 20-30 ppm of CYA in the pool as that is what seems to be recommended on this site.

The water has been changed and I have just been using liquid chlorine for the past 3 weeks so there is no longer any bromine in the water.

My next question is that I will need to calibrate the unit (I believe the default setting is either 650 or 750mv) and the pH needs to be calibrated once I match it against the testing reagents. Once I get the ph setting for 7.4-7.6 I am really not familiar with the ORP levels and I have to maintain our FC at 1-3ppm (state regs) and I think I read (either here or in the manual) that the ORP setting may/can be adjusted depending on whether you want to maintain the FC at a particular level vs the ORP at a particular level?

Is that level is affected by the addition of CYA? Since we have a decent bather load and it the pool is heated to 92 degrees I would like to maintain the FC as high as would be recommended? Is 3ppm high enough if the CYA is at 20-30ppm? Again, I am limited by state regs. What is the relationship between ORP and FC levels?

Thanks,

 

[jblizzle]

Note that generally we steer away from ORP dosing systems as they can be problematic when CYA is high, although that is generally for SWG pools.

That said, keeping the CYA down around 30ppm may not impact the ORP readings as much and may work well for you. ORP is very loosely correlated to the chlorine level and and the ORP level is impacted by a bunch of other things, like CYA, temp, etc.

I think what you want to do is get the pool balanced manually (ph, FC, CYA, temp, everything) and see what your ORP readings are and then set that as your target for it to maintain.

Take a look at the [FC/CYA][/FC/CYA]. For a CYA of 30ppm, you must maintain the FC > 2ppm at all times.

 

[Bama Rambler]

Since this is an indoor pool I'd target the CYA to 20 ppm. We've seen few problems with ORP at that low CYA level, so hopefully you won't have any.
Also since it's an indoor pool with a large bather load, you may want (need) to consider a large UV unit to help with any CC buildup. While we don't normally recommend UV, it can help in indoor commercial pools.

As for the ORP level, it's best to make a chart of ORP and FC readings over time to associate the ORP readings with FC readings in your particular pool. You will undoubtedly find out that it's different than the 'normal' reading.

 

[JoyfulNoise]

As this is an indoor, commercial pool, your local health codes control your FC levels (irrespective of CYA even though science tells us not to do that....). For most health departments, pools must be maintained with an FC between 1-3ppm with 4ppm being the allowable upper limit that would cause pool closure. So, definitely add some CYA for bather comfort (20-30ppm would be fine) BUT make sure your system can maintain a consistent FC level between 2-3ppm. Doing that should keep the pool clear of any algae or bacterial problems.

As others have alluded to, your bather load is going to drive your CCs and CCs can become a persistent problem in an indoor pool. Once CCs form, they are hard to get rid of without any UV around. Some of the organic chloramines formed from urea and creatinine (components of sweat and urine) can be very difficult to control without a secondary source of oxidation. If you are not going to get a UV sterilizer for the pool, I would suggest you look into dosing the pool periodically with MPS (potassium monopersulfate or non-chlorine shock). You will have to purchase an extra test kit chemical to remove the interference that MPS causes with FC/CC testing but the addition of a non-chlorine form of oxidation can help to breakdown the urea and creatinine before they become a problem.

Does your health codes state any upper limit on CCs that would cause a pool closure? Many have it set very low, ~0.5ppm or less.

 

[dmccarthy]

Thank you for the replies. As far as our state regs, yes FC needs to be between 1-3ppm and CC is supposed to be below .2ppm. I did install a UV-lamp when I changed the water out last month (paramount 2-lamp system that supposedly handles up to 90gpm as our flow runs between 60-70gpm, so I am hoping it is adequate given our bather load. I have it set on a timer to run for 12 hours/day while bathers are in the water. Our pump runs 24/7 (state reg). So far the cc readings are holding steady right around .2ppm ( i do notice that they occasionally pop up to .4 or so after adding a gallon of chlorine or so the night before) and I do keep several bags of the non-chlorine MPS shock on hand as well. My plan was to keep the chlorine levels at or near 3ppm as much as possible with no more than 20-30ppm of CYA due to that addition of the UV lamp.

Just so I understand correctly (because I have not installed the ORP controller yet and we are still doing manual dosing of chlorine) once I get the readings right where I want (as far as FC at 3ppm) the system (ORP) will be reading what the mv is at that point? and whatever it is at that point 650, 750 and so on should be my set point to maintain those levels correct?

I believe the instructions said it defaults to 650mv and if there is a specific FC level instead of mv that you can adjust it manually.

As far as the test kit purchase to remove the interference that MPS causes could you recommend what that is? I currently just use the taylor test kit recommend on this site for all our testing.

Last question(s) (and probably a dumb one as I will be new to an ORP controller) will I still need to shock on a regular basis with this type of set up or because it is constantly adjusting/adding sanitizer should this eliminate the need? And would the MPS shock throw off the ORP readings at all? As long as everything operating correctly of course.

Thank you

 

[dschlic1]

I seem to have read some place that public pools are not allowed to use CYA. The reason being is that in the event of having to shock/slam the pool, lower levels of FC will be needed. Perhaps consult with your local health department?

 

[JoyfulNoise]

I seem to have read some place that public pools are not allowed to use CYA. The reason being is that in the event of having to shock/slam the pool, lower levels of FC will be needed. Perhaps consult with your local health department?

This was already covered. His local regulations do not prohibit the use of CYA.

Just so I understand correctly (because I have not installed the ORP controller yet and we are still doing manual dosing of chlorine) once I get the readings right where I want (as far as FC at 3ppm) the system (ORP) will be reading what the mv is at that point? and whatever it is at that point 650, 750 and so on should be my set point to maintain those levels correct?

Correct. Figure out how your pool's FC correlates to ORP level and then set that voltage setpoint on the controller. Monitor closely to make sure you're hitting the correct FC level.

As far as the test kit purchase to remove the interference that MPS causes could you recommend what that is? I currently just use the taylor test kit recommend on this site for all our testing.

Reagent Pack, Monopersulfate Interference Remover (for 2000 Series kits w/ 2 oz reagents K-1515-C)

Last question(s) (and probably a dumb one as I will be new to an ORP controller) will I still need to shock on a regular basis with this type of set up or because it is constantly adjusting/adding sanitizer should this eliminate the need? And would the MPS shock throw off the ORP readings at all? As long as everything operating correctly of course.

Thank you

If you maintain the water correctly, you should NOT need to shock regularly. MPS can interfere with ORP because it is an oxidizer and the ORP probe is, in essence, measuring the effect that all oxidizers in the water. SO you may need to shut down the dosing system if you happen to need to dose the water with MPS. Since you have the 2-lamp UltraUV system, I would simply rely on that to help with bather waste and CCs. It is normal for CCs to jump up a little when you add chlorine because you're increasing the amount of chlorine in the water and thereby increasing the reaction rate between chlorine and ammonia. You'll know there is a problem when you add chlorine but the CCs levels don't go down. In that case, you're battling organic chloramines and often the easiest solution is to do a partial water exchange to get rid of them.

 

[dmccarthy]

Thank you for the replies. I will order those reagents and see if we are holding cc below .2. If I remember correctly I believe someone said that the 2-stage SeaKlear PRS clarifier (which we have) can also help a little bit if we are having issues with cc as well?

Thanks

 

[JoyfulNoise]

The 2-stage PRS system is just a clarifier that helps with cloudiness and is useful is reducing the chances of cryptosporidium transmission. It won’t do anything for CCs.