I'm going to have to agree with many of the others here. Monitoring would be fine, alerting on out of bounds conditions would be good too. Automating those chemicals is a bad idea for your pool. PH is tricky to control as there are so many variables that change the way it behaves.
Usage rate being the big one (consistency of use makes it easy), next would be sunlight, then temperature, and then there are the ugly contaminants we don't like to think about (grass tracked in, dirt tracked in, hair shampoo, and .... it's gonna happen ... bird droppings) all those go into how often you need to mess with chemicals. When it comes time to make a change, do it when there is time to correct but you have enough time to let it work. How long you should wait in the "measure, change ... wait ... measure" cycle depends on the "turnover rate" of you pool pumps. When I had my hot tub (more of a pain than a pool because of the temperature) my rule of thumb was let all the water turn over twice before you decide to make a change again or not. As someone else also mentioned it's really easy to over correct, in either direction. If usage and the other things are reasonably consistent you will get the hang of it pretty quick. So for the first week or two when you are learning try to maintain consistent use while you learn the tricks of the trade.
For many moons I was an industrial controls engineer for a large food company, The only thing harder to control (in the food business anyway) than PH was color ... How brown to you want your chocolate (because it's really an off white cream kinda color) or how red to you want your strawberry ice cream. Other than color PH was the biggest pain, really expensive to do on industrial continuous process systems too.
Not so expensive for pools, but manual is the way to go. But by all means ... Enjoy the pool!
i actually disagree with most of the people on here about this. There are not many people who own a pool and are ever happy about having to maintain it - it is always hard work.
Most people will go out once a week (on the weekend) and run the pool tests (however you do it) - notice that something is out of whack and then add the appropriate chemicals (acid, chlorine, Buffer etc etc) - BUT they will do it in a big dose to hopefully bring the pool back into line for another week - if they or the kids are going to use it that day they will (maybe) test again later that day after running the pump to see if it has been effective. If the kids friends are coming over - probably add extra chlorine and when they have finished throw in a handful (or bucketfull etc)
With a system like Barts proposing - it is microdosing and probably on a continual basis and then measuring the success of that and adjusting as it goes.
I assume he will be using 20litre (or less) drums of chlorine and acid - so the chance of anything dangerous happening is almost nil - it also appears that the system introduces the chemicals into the water that is flowing through the filter or on the way back out - so it is going to be well mixed and of a very low concentration (microdosing)
Based on Barts level of attention to detail that we can see with the stuff he does on here i think this will be a winner.
Bart - there is an Australian company that makes an Arduino with Ethernet, microsd and RTC inbuilt - this might be of interest to simplify this project (if you go down that route rather than through a RPi) - the product is called the Ethermega
Something I havenât seen mentioned above yet, I genuinely donât know if it matters in this case, is the size of the pool. There were a few measurements thrown around about 50m3 volume pools and the like.
Looking at the size gives at the store youâd get about 17.5m3 for this one, But looking at the further specifications you will only be able to use about 12.5m3 of that. Which means itâs much smaller than just about anything mentioned above. Should/will that have an effect on the measures/solution?
it was mentioned earlier in the thread as to the volume of the pool. Although i have not looked at the code i can not imagine that you would not be able to put in the actual water volume somewhere - having said that - as you are only using a small slow pump to microdose i would imagine the issue of overshooting would be minimized - it would almost certainly be running on some form of PID algorithm
Since I know myself in the pool I have several things to say:
Priority to filtration. the quality and ease of maintenance of a swimming pool depends on filtration. As has been said, the small pumps provided with these pools are "gadget" the filter clogs very quickly and harms the quality and renewal of water don its quality = change the pump by a sand filter system and small pump like this one for example: https://www.intex.fr/shop/filtration/3564-filtre-a-sable-4m3-h--6941057415499.html.
Treatment (measurement and disinfection) and filtration must be done during the day: bather + sun = water pollution. At night, not much happens and the sun does not destroy the chlorine present in the pool.
Yes, the pH does not move much once balanced between 7.2 and 7.4 BUT after filling the pool it will go up very quickly (at least here in France hard water so high pH).
To start and take your first steps in the pool: you need to measure the chlorine and the pH with strips or drops like this: https://www.amazon.fr/Manufacturas-Gre-Testeur-hydromassage-ExpĂŠdition/dp/B07PB2LX2Y
a float like this: https: //www.amazon.fr/Distributeur-thermomètre-applacteur-automatique-dÊsinfection/dp/B07SVYWDVX
: you put a pebble of chlorine in it and let it diffuse. There's even the built-in thermometer!
and a bucket of pH corrector + or - powder, according to the evolution of the measurements and your pH of the water.
And above all, clean your sand filter once a week by acting on the backwash valve of your superb filtration.
You will be able to see how the water in your pool evolves day after day.
To go further: Node-red? Yes, you could do everything with Node-red: pH, temp, redox, and more ...
Each pH and redox probe measures milivots. It is enough to transform the mV into pH according to a curve. The redox will be the measured value ex: 600mv is a correct disinfection rate on average. It all depends on the mV of your original filling water.
CAUTION: as read here, certain probes have an electrical link with water: pH and redox measure the mv in water, so they must be isolated from their mass. Either using an isolation circuit (power and signal), or make an electronic card with several transformers. A Transfo (230vac => 5vcc) for the Redox function and a Transfo (230vac => 5vcc) for the pH and Temerature function. As such, the power supply to the circuit and the measurement will be isolated from each other if they are in the same liquid.
This is THE delicate part of the project!
The temperature probe is electrically isolated from the water so no need for an insulation circuit. I recommend a cheap, waterproof DS18B20 sensor probe, in "one wire" very easy to connect to the RPI (as you have already seen): Display temp (18b20) on oled with just pi and nodered
You could already start with this is the simplest.
Which sensors to buy: expensive, not expensive? No matter, they are all made in China lol It is not because it is more expensive that it will last longer ....I have less scruples to renew every year, a pH probe at 10 ⏠than a probe at 50 âŹ
Where to place them? : On the piping, in line after the sand filter with a bypass system as you have already shown, it is ideal.
The software: these pumps have a flow rate of about one drop per second (1.2l / h)! No need to make a complicated program:
Ex: if you give a pH set point at 7.2, and your measured pH is at 7.3 you start injecting ph-liquid (20L can or less, you will see), as soon as your measurement is at 7.2 you stop d 'inject. You will see later if you need to add timers to limit the duration of pumping of liquid, but not necessary.
Investing in quality filtration guarantees you ideal water quality and product regulation.
Even if the suction and discharge of your filtration are not very far apart.
It's already been a lot, good tasting.
[EDIT] I forgot an important thing @BartButenaers : think of leveling the ground in general they recommend to put a layer of sand: Do not forget that you have 12 Tons of water in your garden ! (look at your water meter before and after filling will give you an idea of the volume).
And protect the bottom of your pool against peaks that could puncture your waterproofing, a leak would add more maintenance concerns
