ORP Readings vs Chlorine Reading

[Peedub20]

Hello All,

New to the forum and to having a pool. We recently had a fiberglass pool installed. They began in October and recently finished due to the weather.

When we test, we are consistently seeing very high chlorine readings, usually 10. We asked the installer, they came and looked at the panel, read the ORP, which is at 650 and said all is fine. I don't believe this is correct, but it very well could be. If this is indeed incorrect, how do we go a out adjusting the chlorine level down when the ORP is reading appropriate?

I am sure you may need more information about our system. We have a Hayward Aqua Plus automation system, which has a turbo cell installed. pH is readying at 7.5 and alkalinity is sitting at 110.

Apologies in advance if enough information has not been given.

 

[mknauss]

Welcome to the forum!
We have found that ORP is not viable in outdoor pools. The low CYA you must maintain does not allow for consistent FC management.
You are welcome to search the forum as others have come here with much the same issues.
I suggest you read ABC's of Pool Water Chemistry and consider reviewing the entire Pool School eBook.

 

[Divin Dave]

Hi Peedub,
If I dont tell you, someone else will, but ORP's are notoriously inaccurate. The reasons vary and are many. This is why us here at TFP only recommend drop based test kits to test our pool water with. We dont have to worry about the CYA affecting the ORP and providing inaccurate reading and we dont have to worry about the ORP being calibrated.

But to answer your question, the FC will come down on it's own. People in the pool, organic stuff in the pool and UV from the sun all will use up your available FC. For the FC to come down, you have to remove whatever source of chlorine you are using. Pucks, Saltwater Chlorine Generator, Manual dosing or whatever it is that adds chlorine.

Depending on what your CYA level is, a FC of 10 may be just fine. Did you know that your FC should be based upon your CYA level is? as posted previously, the ABC's in Pool School will tell you this and provide a table of recommended FC levels for varying CYA levels, and much more about all of the different pool water parameters! Check it out when you get a few spare minutes.

 

[Peedub20]

Thanks, guys. We are kind of learning on our own and greatly appreciate the help. CYA is 40.

I was scrolling through the setting/diagnostics on the AquaPlus automator and it had the ORP set at 650. As I'd scroll through, it would note that the chlorinator was off as the ORP was met. If this is the case, do I simply need to adjust the ORP so the FC comes in line with the CYA and does not continually keep chlorinating to reach the 650 ORP?

Thanks again, really appreciate all the feedback and help. I am reading through those ABC's now, but thought the above might be a good question beings it was actually equipment related.

 

[Divin Dave]

its OK Peedub, we all had to start new too! So we're here to help if we can.

with CYA 40, your FC top end recommended level should be 11.5% of that. (and let the minimum be 7.5}
so about 5 or 6 should be your target FC. If the pool is used a lot on a daily basis, even 7 would be OK cuz a lot of FC will be consumed by the bather load.

With FC of 10, you are right at the max of what. TFP would recommend as a safe level to swim in. Its ok, but no higher. (24% of the CYA).

What you need to do is one of 2 things or a combination of both.
Lower the Pump run time, as the SWG doesnt work when the pump isnt running,
or lower the SWG output. Or a combination of both.

Figuring out the output and the pump run time is a bit of trial and error. Likely the easiest thing to do is just lower the output. Start by reducing it say, 10%, give it a day to level out and check again. Then check it every day and make necessary adjustment until your FC is at the right level . Dont be surprised if it takes a week or so get it about where you want it to be.

 

[Peedub20]

So, I got my Taylor K-2006 test kit and completed all the tests. Test came back as follows:

FC - 20 (YIKES)
TA - 110
CYA - 60
PH - 7.2

I have turned the ORP down from 650 that the pool company had it set at and have it now at 500, so I believe that will keep the chlorinator from kicking on, correct? I've also turned the pump to only run a couple hours a day. Hour in the AM and then an hour in the late afternoon.

Anything else I should be doing or that I can do to expedite the FC level down? If I am doing my math correctly, I need to get FC down to 7 to meet the 24.5% of CYA.

I don't know if this makes a difference, but beings the weather has been in the high 70s mostly, the heater is set at 85 for the time being.

 

[Donldson]

We consider FC level to be safe between your minimum and SLAM value. Since SLAM for a CYA of 60 is 24 you are within that limit. No need to do anything but allow it to come down naturally. Trust me, the buffering effect of CYA is pretty significant, the water will feel less chlorinated than your typical public pool.