Pool Arduino controller to read pH, ORP and temperature

[Teapot]

If your sensors are mounted in the main flow stream and not as most pro kit is in a separate slower flow chamber it is quite likely the probes generate a lot of turbulence around their tips causing the noise.

[paulr33]

the ph sensor is reading good values, checked against calibration and chemical (droplet) test but the ORP values are off the planet. im reading on average, -200 to -400 for ORP which from what ive seen is way off a reasonable baseline of 550 to 600. My alkalinity levels were low (80ppm) so I added some increaser and now my alkinlinity is around 130ppm which is in the good range and my Ph shifted a little so ive brought that back down to 7.6 and now awaiting to see what ORP looks like. Free chorline looks good around 3ppm.

maybe the ORP sensor is toast? ive ordered a seperate ORP pen sensor to see if my pool is off the planet or the sensor is dead/out of range.

[paulr33]

yes you are right, re: samples and i am ok with that as i can make code for my graphing engine that means it only captures and plots data during non-pump running timeframes so thats not an issue for me, and the whacko readings im posting up are when the pump is off also to rule out interferance. the only thing im not doing is sampling one sensor at a time, the code is active for both sensors and both are running in real-time and the documentation talks about avoid electronic interferance so i could change the code to sample Ph then turn the sensor off then sample ORP then turn it off and back again, whereas currently both sensors are always powered on and active

[Teapot]

Paul, I noted you said you have low Alkalinity (80ppm) Your pool is fiberglass and therefore you can run with your alkalinity much lower, this will help stabilise the pH around the usable figures for our pools (7.2-7.6) providing you are not relying on pre packaged tabs for chlorination?

My pool, (vinyl liner) runs around an alkalinity of 37-50ppm with near rock solid pH and less acid needed when pH correction is required. The higher figures used by the industry were born from concrete pools that require it. In effect you are over dosing causing a higher build up and more out gassing of CO2 which causes the pH to rise.

If using tablets to chlorinate you could get pH fluctuations using lower Alkalinity as they are made with higher alkalinity in mind but it's not needed.

[paulr33]

hi teapot, thanks for the reply so quickly. i use liquid chroline when i add it as its directly active and easier to use/handle. we have a pool tech come out once a year and plan on doing it each year and he said our alkalinity level was low also and said it should be around 80 to 120ppm. once i get this other ORP sensor I can then do some comparisons as the values im getting make no sense. the last tests i did today were free chorline 3ppm , ph 7.6ish and alkalinity approx 130ppm but yet ORP comes out at -439 - doesnt make sense!

[Teapot]

Hi Paul, Your pool tech is just regurgitating what he learnt in pool school and most all books on the subject. Sadly these are all out of date. I even questioned two chemists who stated "your pH will drop off a cliff" Oh how is that? I asked. To have the pH drop off a cliff implies that a chain reaction would take place, would it I asked. They said no. For each measured amount of pH- the pH falls, without a big buffer (Alkalinity) it falls easier (cheaper to) and doesn't try to fight it's way back up. Bicarbonate of soda dissolved in water has a pH of about 8.1 to high for our pools. The stronger that 8.1 buffer is the harder it is to move and the easier it is to rise back up again. NOTE this is for liner and plastic/ fiberglass only and not for concrete! In case others read this.

Back on track, what level is your CYA stabiliser? this can easily wind down the REDOX figure.

[paulr33]

ok did a heap of troubleshooting and found two issues, the 5v reference point i was using was wrong so the scale was way out and secondly the 5v PoE adapter i was using didnt have enough juice to run the temp sensor, ORP sensor and PH sensor so direct 5v USB and it works first shot.

i now get Ph of around 7.6, ORP of around 195mv and Temp of 25deg (c).

I now need to watch a few days of ORP and see what the data looks like and compare my other readings such as CYA and double check alkalinity but its looking promising, still a long way from ideal 600+mv for ORP.

[paulr33]

check out the logged ORP data, i am certain the sensor is damaged, $190 AUD for a new one

[Teapot]

Hi Paul, You should be able to check the voltage off the back of the probe if they supply any data with it?
What is your CYA level?

[paulr33]

im certain the sensor is dead so ive asked the manufacturer for a replacement. the CYA levels were low and i added some stabiliser and brought the CYA levels upto around 50ppm. all the other chemicals look about right and at reasonable levels.

[Teapot]

Ah, it's much easier to get things set up without the interference of CYA. If your gut feeling is the sensor, then you are most probably correct. I and others bought some of the cheapo's from Ebay which do work after a fashion but soon go completely off. I think they are meant for non chlorinated water maybe fish aquariums.

[paulr33]

yeah ill go for a replacement sensor, i had it working at home when i first got the sensor as i remember testing the code etc so yeah its damaged i would say.
the sensor is $190 AUD as its rated to ~100psi and industrial rated hence the added cost. their lab sensor is about $70 AUD but I figure im going to get a few years out of this sensor so may as well do it properly

[paulr33]

replacement ORP sensor on the way, should have it next week

[paulr33]

new ORP sesnsor arrived and all good, installed and working, pool water is 680mv at first sample
will get a weeks worth of data plot it up

[paulr33]

some initial data from pH and temperature

you can see our solar heating works wonders when the sun is heat, no problems running it around 28deg and maintaining that level. perfect for all day swimming with kids

we had an awful amount of rain on the 28th of JAN and it's skewed out the pH a bit
you can also see the daily effects of the salt water chlorinator slowly increasiong the pH day by day

the reason for the pH staircase chart is because i cant sample pH while the pump is running at it skews the data it captures. the vendor reports pH and ORP should not be sampled while pumps are running. so my pump runs from 10am to 4pm so i sample pH for a window of 1 hour so thats why it looks like a staircase. this is fine for my appication as im more interested in the weekly trend as opposed to the daily value