One other thing to add is that the Notecard itself includes 10k pull up resistors.
The datasheet for the EZO DO shows it also includes 4.7k pullups, and similarly for the EZO PH and the EZO EC boards. This is in addition to that the 10k pullups on the Adafruit logger.
This calculator shows the effective resistance of the 5 devices connected in parallel on the bus. When you plug in the numbers, you’ll see an effective resistance of ~1.2k Ohms (1.19 to be exact). This is much too strong a pullup (that is, the resistance is too low) which will mean the individual I2C devices will not be able to pull the signal low.
If you were to use the TX/RX serial interface with the Notecard, that would give an effective resistance of 1.35k Ohms (10k, 4.7k, 4.7k, 4.7k), which is still too low of a resistance, creating a strong pull up.
I suggest you remove the pullups from the EZO boards, leaving just the two 10k pullups from the Notecard and the Logger. That gives an effective resistance of 5k, which is much more in the ballpark of what’s needed.
I hope that works out for you - please let me know how it goes!
Thanks,
mat.