I made one of those. Background I'm a salt water tank enthusiast. I wanted something sophisticated so I could automate many of the dull tasks. I started with a Arduino Mega as the foundation. I added an ethernet/SD card shield. I added PH and TDS probe I2C modules from Atlas Scientific and a RTC module (temperature compensated for accuracy).
I then built a bus based on RJ45 connectors. It had 1 serial, 1 1-wire, I2C, and gnd/+5.
For power, I purchased one of those 8 channel DJ power centers. It's just a glorified power strip with the ability to manually turn on/off each individual plug. I created a I2C 8 channel relay module that I piggy-backed on the power center and wired it in.
For communications, I added two RJ45 jacks wired in parallel. This allows me to run standard CAT 5 Ethernet between it and the Arduino while leaving a jack free to daisy chain to another power center if I so choose.
On the power center I plugged in the following:
Main lighting
Moon light
Left wave pumps (for wave motion control)
Right wave pumps (for wave motion control)
Skimmer
Heater
Dosing pump 1
aux
So in total, I had the following talking to the Arduino:
8 channel power
1 wire thermometer
PH
TDS
Clock
Keypad
LCD
The application ran a sequential timer system along with the LCD update and keypad polling algorithms. I integrated calibration routines in addition to everything else so I could do the three stage sensor calibrations (low/med/high solution calibration). As far as the dosing pump goes, it was only doing kalkwasser top offs. But I could easily done PH adjustments. But I found the kalkwasser did fine. The whole thing logged to a simple web page so I could monitor everything over Ethernet. It stored the logs on the SD card in CSV format so I could dump it into a spreadsheet and view the trends.
Yack yack yack...if you have any questions, let me know.
