pH level cycle

[djbilo]

I attach 2 photos from the device I have had installed which automatically measures Chlorine and pH levels and injects muriatic acid and liquid coloring as required.

The chlorine levels stay nice and even but the pH levels are cycling as shown in its monthly view.

The supplier of the device has no logical explanation for this behavior in the pool water pH.

I have my concerns about the rather wide level fluctuations and also have theorized to the device supplier’s team (this company invented the device so their engineers have also loooked at this. They had a replacement motherboard sent out to be installed by their tech, with a couple of key fixes and upgrades in the new board.

I wonder if this cycle represents the natural cycle of water pH for some reason (does not seem related to our rain patterns here in the DFW Metroplex) or possibly the device having trouble keeping the pH within its upper and lower limits.

They come out about once a month to replenish the chemicals, check the water chemistry and rebalance manually if needed. One time the tech made an error and over-added acid but that was when the old board was giving inaccurate readings.

My TFT tests mirror what the sensors reflect whenever I test the water, so now it’s down to either some underlying residual issue with the pH part of this system, or a cycle of pH like this from something happening in the water or the plaster surface which I cannot “see”.

Any thoughts? Thanks in advance.

 

[Newdude]

Do you run anything that would contribute to the PH rise ? A spillover or bubblers perhaps ?

Have you increased the acid dosage to counteract the weekly PH rise (that's fairly normal) ?

What's your preferred PH target and why ? When pools aren't stable in the lower 7s, we usually reccomend targeting higher 7s.

What's your TA ? Is that high and contributing ?

 

[djbilo]

No spillover or bubbler. Only the submerged auto vac (Barracuda). The device’s target range is 7.5 to 7.8. It is overshooting on the low side. TA is in the 80 to 100 range last time I checked.

With this device I do not add anything. The device does the work. (see CUA Pools | Pool Service Company for more info-not a commercial nor endorsement, this is what I had installed in February to buy back some time.)

 

[Bob Jakob]

Looks like not enough time allowed for pH to stabilize after an acid addition. When pH reaches high set point it is overshooting the amount of acid needed.

 

[Newdude]

TA is in the 80 to 100 range last time I checked.

7.5 to 7.8

Try it at 7.8 to 8. It will likely be more stabil in the hugh 7s.

 

[dschlic1]

pH is sometimes hard for automation systems to control. pH is actually a log of the parameter that is being controlled. This means that the system response to a pH change is very non linear. Is the plaster new? New plaster can and will cause large swings in pH. The other thing that might affect pH is the addition of fill water. Can you see if the pH swings correspond to when you add water to the pool. What might be happening is that when water is added, the ORP goes down and then more chlorine is added. That can affect the pH levels.

 

[mgtfp]

Could it be that the acid doser is expecting diluted acid, but you topped up with full strength muriatic acid?

Also looks like the probe doesn't measure below pH 6.5, it seems to have been much lower there. But to get there, you needed a very low TA, which is not in line with pH rising above 8 in the first place. I also suspect that a badly calibrated pH probe is adding to the problem.

Step 1 seems to me to calibrate the pH probe.

 

[djbilo]

Turns out….

The tech sent to replenish the chemicals has been adding a big dose of acid to the pool at the same time.

When all else fails, check for the obvious but illogical actions hiding in plain site.

The company is going to re-emphasize to its techs to let their system do the work. What a concept.

 

[Jaffles]

I have had two auto dousers over time with an existing pool and new recent build.

To my mind and experience the system works great if the probes are fine. By that I mean calibrated correctly, and CYA is under 30ppm. Any higher CYA and it tends to coat the probes so they read incorrectly. Then its anyones guess what will happen. Calibration and cleaning is easy but should be done quarterly.

Acid, well with my Astral branded system suggest should be mixed 2 to 1, 2 is the water. You can use straight acid but its hard on equipment. Currently the PH of the new pebble pool is 7.8, come down from 8.9 over the past 4 weeks. I am shooting for 7.3 and have been adding 1.5lt acid a week to lower TA and stabilise PH. The system has been dousing about 2.6g to 3.9g (10 to 15lt) of diluted acid over 7 days. 22500g (85,000lt).

To me your ORP is pretty high in the high 7 into 8s. So that's a lot of chlorine. I have always shot for 720 ORP, it rarely seems to gets there often achieving around 680ish on 1750rpm for 9 hours in summer. I am meant to lower it in winter but really the system just douses less left at the summer level. The pool is crystal clear and inviting. Actually the only time I have had an issue in 5 years of pool ownership was with a CYA coated sensor.

If the pool gets smashed over a day of activity and you have to back it up the next day, or you have a sense the water is not as clear as before; I just run the system for longer or over night on low, 900 RPM. All is well in the morning. Or if the system is set on AI (artificial intelligence mode) it automatically just does it. It sorts pump speed, run time, dousing rates.

My TA is 80, CA id 475, about 250 to high at present.

Glad to read you (or the pool shop) seem to be on top of it.