Need help with auto water change setting on DA ReefKeeper Lite

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I'm using a RKL to try and automate a water change. What I want to do is use the standby mode to initiate the change at will. I want to start it with a 5 minute run time (to empty my sump) and let a pump run, then when it goes off, I want the ATO to kick on (which was set to OFF when in standby mode) and start filling up my sump. If I time it correctly, this will work well!

Technically, this seems possible, but I dont know what to set the water change pump up as. I've tried a few types, but none of the settings I tried allowed me to activate the pump with just the standby feature. I dont really want it to run at all unless in standby.

For example, if I chose on/off and set it to off, it wont activate in standby because the OFF overrides the standby function. Or if I chose a light with a one second run time, it didnt seem to work. I'm trying to trick it into working just in standby, but it doesnt work. I'm wondering if anyone has done anything similar?!

Thanks for any help.