The optic cell will be flushed with pool water and then a sample will be taken roughly 15cm below the surface with a small dosing pump. Even smaller dosing pumps will be used to add the required chemicals and titrate the solution drop-wise. I believe a pump per chemical will be more economical than trying to use solenoids and having to flush the chemical lines every time.
For the spectrometry I will be using a low power red laser diode and a photo diode. Measurements will be taken of the clean sample water to establish a base line before every test. Then as soon as the titrant is being added, values will be taken after every drop, until a colour change is noticed. In case of tests where colour should be read, an approximation should be able with a red laser alone as most colour changes should be able to be seen in red light. If I do struggle I will add other colour lasers as well, or try LED's
Taking measurements still means nothing if I have to go take the unit out of the pool every day. So I will use a 315MHz transmitter to send the data out after every measurement. An ATmega will run the show, turning the pumps on as needed to flush, rinse, sample and titrate. For now communication will only be one way, so the ATmega will be programmed to take measurements at certain intervals. Certain tests needs to be done daily, others weekly and the Chlorine level should be taken right before you swim preferably to determine if it is in a safe range for kids. Later better tranceivers can be used to incorporate a polling option.
The base unit will use a 315Mhz receiver and an ATmega. It will constantly show the property levels. 3 LED's can be used to indcate if you have to increase a property, decrease it, or if it is in range. A small OLED display may be added later to show the exact values of the properties, as well as the correct amount of chemical to add for your pool size.
Maybe I can add larger dosing pumps on the side of the pool to dose with bleach, bicarb and acid to correct the major properties automatically on a daily basis. Now that would make a care free pool that only needs to be baby proofed.