Nice! Can you tell me more about the storage tanks you are using? I am having trouble finding the right fittings for the tubings, but I think they are available online at McMaster-Carr's website. Do you have any other source for those fittings that go from the 9-10mm tubings to a 1/2" or 3/4" PVC?
Are those some kind of sensors with blue and red caps on a bypass line between the pump and the filter?
I believe I'm just using polypropylene fittings, they have good compatibility with both chlorine and muriatic acid. I bought some from McMaster, but I also bought some from Amazon, I don't recall which ones these are. This has been a work in progress for several years.
I bought the tanks off of Craigslist/Facebook Marketplace, I believe they are originally out of a car wash. I drilled a hole in the small caps and threaded the tubing through them. On the inside of the tank I'm using some glass tubing I found that the tubing fits on and holds the tubing to the bottom of the tanks. I purchased the warning lables off of Amazon. The Acid tank is a recent addition, before that I didn't worry about the warning labels since I knew what was in the chlorine tank and I wasn't worried about someone putting the wrong chemical in it if I needed to have someone fill it when I was gone. The sensors on the Chlorine tank are liquid level sensors, I have sensors at the 3, 6, 9, and 12 gallon levels. I'm also adding sensors to the Acid tank at the 5 and 10 gallon levels.
The red and blue sensors are Atlas Scientific PH and ORP probes, I use the EZO modules to interface them to the Ras Pi (btw when they say don't use perf board to connect to the EZO modules, they mean it). I'm not using either of the sensors to directly drive chemical feed, I check the PH and add as needed, and I use the ORP as a an indicator to tell me if I'm way off when I'm not able to be home, so for instance if I'm 900mv+ then I can probably reduce the chlorine I'm adding a bit and if I'm <600 I need to increase it some This is just for when I'm not home to do normal testing. I have a cron job that adds a fixed amount chlorine on an hourly basis, and I adjust the total by modifying that cron job. Last summer I had to be away from home for a couple of months and everything stayed sparkling, but when I got home I found I was higher than I wanted to be for chlorine, so I added the ORP probe. When I'm home I use the TFT test kit and adjust as needed, but that's difficult to do when I'm 1,000 miles away.
Other sensors in the picture are a flow meter, a pressure sensor, a water temp sensor, and a water level sensor. I'm expecting a PCB this weekend that will be replacing the perf board based system I am currently using. I'll also be upgrading from a Pi zero to a Pi Zero 2 which should allow me to install the current version of the nodejs poolController software. Once I get that installed I'll make a post with some more pictures, and a better description of what I've done.