2it,
The amount of chlorine that your SWCG produces is based upon two things... One is the output percentage and the other is pump run time.. So, the cell will produce the same amount of chlorine if it is run at 100% for 1 hour or 10% for 10 hours... Without an automation system, you set the output% to more than you need and then simply reduce the pump run time down to what you need to make the amount of chlorine your pool uses each day. In your case, you can set the cell to 20% but run your pump longer, or set the cell to 40% and run the cell less.. Whichever works best for you.
I find that it is easier for me to run my FC a little on the high side.. This means that if I skip several days between tests, I never have to worry about letting my FC drift too low.. How fast the FC gets used is based on your CYA level.. If the CYA is low the FC will get consumed quickly..
An EasyTouch or the new IntelliCenter will control your SWCG in 1% increments instead of the current 20%.. If you can install a new electrical outlet or add a 220 volt dryer outlet, you can install an automation system. That said, trying to retrofit an old pool with an automation system, is much harder than installing one as the pool is being built..
I am an automation kind of guy, but I would recommend you initially try to control your SWCG using the output% and pump run time first, before going down the automation path.. I suspect it would cost about $2K to install an EasyTouch and ScreenLogic if you did it yourself..
Some advantages of an automation system are...
1. SWCG control in 1% increments
2. Pump Speed control
3. Heater control
4. With ScreenLogic you can control things via your PC, phone, or tablet.
5. Automated valve control (assumes you have a water feature or spa)
6. Scheduling can be done at your PC rather then at the pump.
7. Automated light control and color (assumes you have a color LED lights)
Thanks,
Jim R.