SurferTim:
I thought this would be fixed by now. Do not use 3 exclamation marks ("!!!") in a row in your code. It puts the bootloader into a debug mode.// change this
Serial.print("pH LOW!!!");
// to this
Serial.print("pH LOW!");
It's a function of what bootloader was installed by the original manufacture of the board. So while the newer (fixed) bootloader for the 2560 is distrubutived with the IDE that doesn't mean that it made it into any user's specific mega2560 board. I suspect that many boards shipping today might still contain the older mega2560 bootloader, depending on source of purchase, shelf time of the board, etc.