Some of the digital timers you can buy will allow you to program them to run on specific days of the week. The one I have has an option for Mon, Wed, Fri. I suppose if I used another one and offset the date on it one day I could achieve the opposite days setup. However that requires two timers as opposed to just having both my dosing pumps plugged into the same timer. This saves a couple bucks since those fancy digital timers start at about $20 and go up in price from there.

When automating my tank I was trying to use as few components as possible with the thinking that the fewer items I used the few things there were to fail in the system.

And there is always keeping the wife happy, who was getting a little irritated by the amount of money I was spending to automate..