I've got a static system also (Water softener- RO - Double DI), my thing I haven't been able to work out is I run water through the RO to the waste water tank for ten minuets before I switch it over to the DI's. This is because there is a lag until the the TDS reading comes down post RO, as the RO coughs out a load of poop when it's been idle and so I can prolong the life of the DI resin. Is there anyway this can be automated (i.e. it won't let water into the DI vessels until say it reaches 25 TDS)?