Pool Arduino controller to read pH, ORP and temperature

[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

[paulr33]

i have the opposite problem for the water temp sensor, i can only sample that reliably when the pump is running otherwise because of where the sensor is, it gets skewed by the air temp and temp of the water in the pipework, no where near the pool. so i made some code changes to;

plot temperature during pump run cycle - 10am to 4pm
plot pH 1 hour after pump stops - 4pm to 5pm
plot ORP at 11pm at night after 5 minute pump run to get fresh pool water from pool

[Teapot]

Good stuff Paul, nice to see the ORP up near where it should be. That pH spike at 7.95 ish. If you bring down your alkalinity closer to 40-50 buy adding acid and then aerating to raise the ph back up and repeating until you have a lower alk figure you won't spike so easily. We don't need that much alkalinity, the pool water is still super saturated at 40ppm with bicarbonates at least 7x more in the water than the air but it will reduce the speed of the rise.

[paulr33]

some initial ORP data
i had a look at the commerical PH and ORP sensor for my chlorinator is about $1000 AUD and the sensors and arduino i got cost me about $400 and i dont have to worry about the system making the pump run flat out if it cant get a magical ORP reading so i much prefer this way.

[paulr33]

ORP

[Teapot]

That's looking better Paul, later on when it settles in I would like to know how much the strong sun has an effect on the ORP. Can you link the pump Doser up to see how often it runs?

[paulr33]

managed to finally get some useful sample data over a period of time, approx 2 months of data +/-

the ORP, PH and temperature are all sampled when the pump is running, so from 10am to 4pm each day. i capture the 5 minute reading from each sensor then compute a single average for ORP and PH for the given day using this data range. i do that so that i have a useful trend over a period of a week, otherwise the 5 minute average plots i did originally dont really help give an indication on a week view whats going on (up or down). so i favoured a single snapshot of the day, based on this 6 hour 5 minute data capture for ORP and PH.

temperature;
this is solar heated, in melbourne australia during summer - although a slightly cooler summer this year

ORP
you can see initially my ORP was too low and i kept getting sight green algae in the corners of the pool so i had to add more salt, alkaline and ph buffer accordingly to bring it all up to normal levels, around 650ish ORP, i havent seen any algae since hovering around 620+ ORP

Ph
the water here is pretty hard so each time i top up the pool, i need to rebalance and bring ph down. i find the ph constantly creeps up each day slowly over a week when its a hot week and the pool cops lots of afternoon sun. need to balance with stabiliser and ph down to recover

[Teapot]

Hi Paul, all looking good so far, do not worry about your pH to much, all within target.
More important is your CYA stabiliser, what is that level?

[AndyFrew]

Hello...as per my knowledge Redox is not a very accurate measure, the cyanuric acid stabiliser plays havoc with the reading.
Better to get the correct level of chlorine relative to your cyanuric acid level and then take the redox reading and look for a consistent levels with temp and pH also.

percentage calculator

[Teapot]

Yep that's the best way to analyse it.