Hi Gagan,
As far as doser pumps, I’ve already done a write up on how to convert 220V Stepper motors for doser pumps into HA controllable, removing the need for the older micro controller they previously were provided with. I also provided the code I threw together to provide the User Interface elements & MQTT side of the solution.
This solution should even work with DC powered motors either with the DC version of the Sonoff 4-gang switch or if you build it from the ground up, 3D printing the dosing components and supplying only ESP chips and motors, and wiring it together yourself.
Of further interest to you, I’ve adapted two 4 channel dosers this way, and One has been installed on the aquarium with great success. The second unit had nothing to do since I stopped with breeding clownfish, so now it waters the backyard flower garden for my wife. I even introduced a binary sensor to indicate when it’s raining, that it doesn’t need to water the flower garden on that day.
Unfortunately, I’ve not had any time or hard requirement to implement EC or pH Tube sensors. My salinity stays pretty solid in place, and pH is measured by the Seneye devices I have. (Bows in appreciation to @mcclown for making this possible.)
I do know that making the hardware for pH meters is esp difficult due to electrical isolation requirements needed for an accurate pH measurement. There are some links to some 3rd party solutions that are prebuilt and made for makers, which are above (I posted about a year back about this topic) which I would recommend you to look at. But perhaps someone else on the forum has made their own pH / EC solutions and has good plans for it and will chime in to help you.
Good luck and keep us posted what you end up finding to go with, so that other’s may also learn from your experiences. 