Here's another MO you might consider that I haven't yet mentioned. It's only slightly related to the acid/chlorine issue. If your ET has any available schedules left. you can add one more. Remember, I mentioned that the IpH, as a safety precaution, only dispenses a small amount of acid per cycle. This is to minimize the possibility of dispensing too much acid at once. Without the IpH, there's nothing to keep the acid pump from emptying the tank except the "off" component of your one-minute acid schedule. If someone inadvertently uses your ET's newly programmed acid button, and leaves it on, the acid pump will drain your tank into the pool.
So with an available schedule, you can create an egg timer schedule for your new acid circuit, with a setting of one minute. Or two, or three, whatever. Some short duration. With that in place, if you push the acid button, accidentally or intentionally, the pump will dispense acid for only that duration. The egg timer will turn off that circuit after the assigned duration. This will serve as a safety cap, but also could be used for manual injection, similar to the way the IpH had a manual injection function: press the acid button and you'll get a minute "squirt." Of course, if you use it for that purpose while the IC is producing, then you're back to wondering if that matters or not...
If I remember correctly, a timer schedule overrides an egg timer assigned to the same circuit. You could test this to confirm. So say you have a timer schedule to inject acid for two minutes. But you have an egg timer schedule that only allows one minute. When you turn on the acid button manually, the egg timer will turn it off one minute later. But if the ET schedule turns on the acid pump, it'll run for two minutes. I didn't test that, because my egg timer duration is the same as my scheduled duration.
Keep in mind that if you want to schedule your acid to inject more than once a day, only that first shot will be in the IC's startup sequence window. Any others will go off while the IC is active. Depending on your IC's output setting, there's still the chance that the acid will inject while the IC is in standby mode, but I can't think of a way to take advantage of the IC's periodic "off" cycle to solve for the acid/chlorine dilemma.
So between the scheduling just after pool circuit startup, and an egg timer, you can mimic to some extent some of the IpH's safety functions.
