Thank you Michel,
The problem is that at the end of the month it goes from 31st to the 1st so scheduling every other day using your system will switch from odd to even days at the end of the months that have 31 days.
The controller I had before had a setting for watering on odd or even days (rain bird) so I was wandering if there is a way to do that with ISY994 and EZFlora.
Otherwise I guess I will have to use your suggestion and switch the days of the week at the end of the months with 31 days.
Any other way?