So I've been thinking. It would be really simple to electronically control the output of the LQ with an ORP driven solenoid valve. Well when I say driven I really mean that the ORP would be the deciding factor to open or close the valve. The ORP would be compared against a percision reference voltage with a basic comparator with a bit of hysterysis. It would turn on at a low point and turn off and stay off once it hit the high point. If the low point was reached again it would turn back on and repeat. The amount of hysterysis would set this window. This would prevent the solenoid from turning on and off too frequently.
Such a control mechanism could have two controls, one for the high point and one for the window of variation desired. A basic power transistor or even a Mosfet could be used to drive the solenoid. Some other support components would be needed to ensure no electrical noise or kick back from the coil. This may be beyond the scope of most in this forum.
I could also see the LQ still having it's control mechanism in place to help prevent complete over chlorination in the event something got stuck. The output could be set to say a bit higher then normally needed to maintain.
Ok, so I just need to find a cheap (inexpensive) ORP sensor and a solenoid valve that'll last in the harsh environment. The rest is cake. I've prototyped and built countless small and large circuits to do various tasks. This sounds like a useful one.
I've checked on the net, I'm only finding pretty pricey ORP sensors. I'm wondering if anyone has any sites that might have some reasonably priced ones.