I just ordered a SL1 module for my RKL basic. This module will allow me to controll up to 2 float switches as well as up to 2 probes at the same time. I purchased the PH probe as this will become a part of my ATO fail safe. I also was able to obtain a simple RKL programm from Digital Aquatics that will allow me to set a predetermined duration the ATO Pump will be allowed to run at any single ATO event. This allows me a third fail safe built into a simple single float ATO system.
This is how it will work: If the float switch sticks and I am dosing Kalk
PH will raise above a determined level and shut off the ATO pump. If I am not dosing Kalk
the addition of fresh water will cause PH to fall and at a predetermined level the ATO will shut off.
Secondly, If the ATO pump runs beyond a predetermined duration of time the ATO pump will shut off.
The variables I must figure out then are high and low PH allowed and the duration the pump will be allowed to run to insure complete filling of the sump but beyond that very long and the RKL will shut off the pump regardless of float, or ph levels. Seems reasonably redundant for safety.