Just to be safe, I want to clarify the use of "If DoW" with the DOS. Please don't use "If DOW Then ON" as shown in my reply above because that turns the DOS head On and it runs continuously the whole day, ignoring the normal schedule and amount to dose. Instead, use "If DoW S-T-T-S Then OFF" in the Advanced tab of the DOS. This allows the DOS to run its normal schedule and dosage volume, except on the days overridden by the DoW command.
After I posted the above example I envisioned you nuking your tank by mistake, so I wanted to point this out.