Did you use the “Address Change” example included with the SDI12 library to give each sensor a unique address? Decagon 5TM sensors are always set to default address “0” when you first use them, so you’ll need to select new ones. I’d suggest something sequential like 1, 2, 3, etc so that it’s easy to cycle through them in the sampling code. How many sensors are you connecting at once? And are you using these with a Mayfly board or some other sort of hardware arrangement?