pH & ORP meter readings fluctuating wildly, & other problems

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BobKat

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May 6, 2014
7
Texas Hill Country
We moved to Texas 2 weeks ago. The house we bought has a pool (built in 2010) that is supposedly very easy to maintain. It monitors the water and adds chemicals as needed, has a Polaris 3900 cleaner. Water and pool surfaces look clean.

This is our first experience owning a pool, so we don't know a lot specifically about pool chemistry (other than the great info I've soaked up here), but I work in medical chemistry and hub is an engineer working in oil refining, so we have strong science backgrounds. We noticed that the pH and ORP readings fluctuate a LOT! pH can read as low as 5.1 then up to 9, all in the same day. (I know 16,600 gallons of pool water is not changing that much that rapidly over and over). ORP fluctuates from about 600-800. pH reading on test strips has been ok.

I took sample to Leslie's last week:
FAC 7.5
TAC 7.5
CH 1000
CYA 100
TA 120
pH 7.8
TDS 1100
Pho 300

Guy at Leslie's said we'll probably have to drain & refill due to CH & CYA, but said we could try turning off the automatic chlorine puck dispenser for a couple weeks, and use Fresh'N Clear (oxidizing shock, 38% potassium peroxymonosulfate), 3 pounds every 3 days. Then bring in another water sample May 13.

So, any thoughts on what might be going on with the pH / ORP meter? (Hub already took out the probes to check for build-up; they looked good.)

Any way to avoid drain/refill? (I read online about reverse osmosis but couldn't find anyone in my area who does it).
 
Welcome to TFP!

ORP is kind of known for strange behavior like that, but PH sensors should be more stable than that. Have you been adding any chemicals through the skimmer? That is sure to cause problems. Also, do you know how old the sensors are? They should be replaced every two years.

By the by, I strongly recommend against even trying to use the ORP sensor. That is much more likely than not to only cause trouble, and even when working it doesn't do as well as more conventional approaches.

If those test results are even close to correct, you are going to need to replace most of your water.

You need to get your PH down right away. High PH with TA and CH at those levels will lead to calcium scaling very quickly.

Then you need to get your own top quality test kit. Knowing what your levels really are is the best possible investment you can make in your pool. Without that you will end up guessing way often and eventually guess wrong about how to treat the water.
 
Welcome to the forum! :wave:

+1 to Jason's post.

ORP Sensors are tricky, very tricky usually. Often, they are very inaccurate. If you are going to use the pH component of the system replace the probe ASAP. They do not last and you don't know it's history. The test kit is essential, even if you are accurately controlling with automation, you need positive verification.
 
JasonLion said:
Welcome to TFP!

ORP is kind of known for strange behavior like that, but PH sensors should be more stable than that. Have you been adding any chemicals through the skimmer? That is sure to cause problems. Also, do you know how old the sensors are? They should be replaced every two years.

By the by, I strongly recommend against even trying to use the ORP sensor. That is much more likely than not to only cause trouble, and even when working it doesn't do as well as more conventional approaches.

If those test results are even close to correct, you are going to need to replace most of your water.

You need to get your PH down right away. High PH with TA and CH at those levels will lead to calcium scaling very quickly.

Then you need to get your own top quality test kit. Knowing what your levels really are is the best possible investment you can make in your pool. Without that you will end up guessing way often and eventually guess wrong about how to treat the water.
Click to expand...

I've been reading on this site for several days, and I have noticed that ORP meters do not seem to be thought of highly here. Why is that? I mentioned this to my husband (mech. engineer and Director of Operations for an oil corp), and he said refineries always use ORP to monitor chlorine, and he considers them very reliable. So I'm confused.

Also, the water in this area is very hard, so I'm concerned that even after draining and refilling, I'll deal with high CH as an ongoing problem. Or do pool refill companies somehow lower the Ca of the water before filling the pool?

No, we've not added chemicals through the skimmer. I assume the probes are as old as the pool, 4 years. They may have been replaced, but I have no way to know. Is there an online site you would recommend for replacement probes, or do I need to go through the pool company that built it?
 
You should test your fill water CH level to get a sense of how much of an issue CH is going to be on an ongoing basis. If fill water CH levels are very high, you might want to try and get by with high CH for a while longer, but chances are very low you could go a whole season with CH that high.

Probes tend to be fairly standardized, but there are a couple of variations so do double check.

ORP probes don't measure chlorine directly, they measure ORP, which is affected by a number of factors other than just the chlorine level. The goal is to try and keep the other things that affect ORP from varying, so the ORP level will correspond to the chlorine level. However, that is often not possible in a swimming pool. This is always an issue to some extent, but is especially true when using a salt water chlorine generator (SWG). SWGs add hydrogen gas to the water, which can have a dramatic impact on the ORP reading in exactly the wrong direction. The probes can also be affected by other factors, like variations in the CYA level, or the use of non-chlorine shock products, or loss of PH regulation, resulting in inappropriate increases or decreases in chlorine production.

In a residential swimming pool chlorine usage is very predictable, other than the occasional large pool party. Most of the chlorine is lost to sunlight, and simple timer based automation is very stable, less expensive, lower maintenance, and not prone to the wild errors often seen with ORP systems.
 
My controller is a CAT 2000, and if I'm looking at the right thing, it's going to cost $400 to replace these 2 probes! Does that sound right?

Also, JasonLion, you suggested I not even use the ORP sensor, but, if I'm understanding my system correctly, I then could not use the automatic chemical system. Are you suggesting I just buy a manual test kit, and manually add chemicals, and forget the whole automated system?
 
Yes, the probes are around $200 each.

The CAT 2000 will work with just PH. You leave the ORP probe you have hooked up but you disconnect the connection between the CAT 2000 and the chlorine feed system. The PH portion will still work.

You will need a manual test kit regardless. The PH probe needs to be checked for calibration occasionally, and if you are using the ORP sensor it also needs it's set point adjusted occasionally based on actual FC levels. All of the other usual numbers needed to be checked and maintained separately in any case (TA, CH, CYA, etc).

I have a similar system from AutoPilot and a couple of years ago I disconnected it. There was simply too many thing that required maintenance and attention on the "automation" system, it was less work and less money to go with the "manual" approach.
 
BobKat said:
I've been reading on this site for several days, and I have noticed that ORP meters do not seem to be thought of highly here. Why is that? I mentioned this to my husband (mech. engineer and Director of Operations for an oil corp), and he said refineries always use ORP to monitor chlorine, and he considers them very reliable. So I'm confused.
Click to expand...

You can think of the ORP systems like cars. a 1965 Volkswagon would be your residential system and a 2014 Mercedes Benz would be the refinery model. They both do the same thing, but one is more expensive than the other and a much better ride. Refineries have deeper pockets than homeowners.

Just my thoughts.
 
There are several differences. First, refineries have professional staff people who are trained to adjust and maintain the equipment, while homeowners expect something to simply work. ORP sensors most certainly require a fair bit of knowledge and regular maintenance, something that is easy to come by in a refinery and not expected in a residential setting. Second, ORP and SWGs conflict with each other. ORP requires low CYA levels and constant levels of dissolved hydrogen gas. SWGs much prefer high CYA levels and constantly add dissolved hydrogen gas. Third, much simpler solutions work just as well. In nearly all cases simple fixed dosage chlorine systems work perfectly well, so well that there really isn't anything to improve on. And water can be balanced to eliminate PH drift in most cases. So what exactly are you gaining with automation? Why spend a fair bit in both money and time to have an automation system, if it gives nothing back why spend time or money?
 

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So, regarding my high calcium (1000), do you think it would be worth trying a calcium reducer (some brand of sodium hexametaphosphate, or even Calgon laundry additive) before draining and refilling?

I got a quote of $850 for draining/refilling, which I thought was really high, then I found out that didn't even actually include the refill water. The pool would be refilled from our own garden hose. So....I'd rather just try to drain myself (probably try a partial drain). We live on a hill, so is it safe to assume the water table isn't going to be an issue? Any tips on draining ourselves?

I'll be getting the water from our garden hose tested (either at Leslie's, or test myself once I figure out which kit to buy). If our water supply has an extremely high calcium hardness (which I'm told it does), would it be helpful to buy a filter for the end of the hose to use while refilling? Specific recommendations?

Thanks!!!
 
None of the calcium reducers work well enough to be useful. In a few areas you can get reverse osmosis treatments (which remove everything including calcium), but it seems unlikely that is available where you are.

Draining is easy enough if you aren't in a huge hurry, especially if you have a spot lower that the pool to syphon to.

The only practical way to lower the calcium level of the fill water is with a water softener. Even a whole house water softener is challenged to deal with the amount of water used by a pool, but it can be done (lots of recharging the softener).
 
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