needing help with automated aquaponic green house

Greetings,

I have read this forum and searched countless articles. I have a Raspberry Pi which I plan to be my main hub (brain) but I think I may need arduino for my sensor readings. This would be my first microcontroller project. I want to measure and log inside and outside temperatures, pressure, humidity, sunlight, and water level of my fish tank. In summer I want it to run a fan depending on temperatures, and a backup heater in winter in case the (rocket mass stove and daytime passive solar pop can heater) isn't enough in winter nights. I would also like to have it divert water from my rain water holding tanks when there is low water in my fish tank. All while logging the information for review and giving me real time control from my smartphone when I am away. I know this is a lot of work for a first time project, but it would make my life a lot easier. I have seen some similar projects on here. I think adafruit would be a good source for materials. And I am fairly technical and have written hex code years ago so with a little help I am sure I can get this done.

Certainly feasible, although as you remark, quite a tall order for your first project. Obviously though, you don't have to do it all at once. Depending on your sensors and the layout of your place, it might make sense to use more than one arduino - to avoid long wire runs or if you run out of I/O pins. How do you plan to communicate with the Pi? xBee, ethernet, wifi, cheap radios?

Take a look at this site - lots of relevant examples: http://www.desert-home.com/.

I'd have the Pi run a web server for your smartphone needs and keep a mysql database with your records and current threshold settings. I'd let the Arduino(s) manage their own affairs, just checking in with the Pi periodically to send sensor data and to find out whether their threshold data had been updated.

This will be of great service. I can look over his stuff.
I forgot to mention some things that I planned on doing. Such as using a sensor to measure CO2, voltage (for shutting some systems down in case of low charge.) And PH anyways. I decided to update with my buy list.
I have been reading Raspberry Pi Home Automation with Arduino by Andrew K. Denis on my Kindle. (Which has some moments of insight, but a lot of concepts are familiar and leave me bored, but I have never worked with micro controllers so I am doing home work.) I guess to get some more beefy reads I am going to have to read some books on python, and c++ sub code.

So here is my buy list (and yes I am being cheap, if I break it, it's an easy replacement. and haven't gotten my relays yet)
PH
http://www.ebay.com/itm/201080663258?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649
Analog to Digital
http://www.ebay.com/itm/190888152989?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649
GPIO expansion (in case I need it)
http://www.ebay.com/itm/400694139624?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649
Voltage sensor for monitoring my solar batteries
http://www.ebay.com/itm/380773553422?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649
Real Time Clock ( I figure I don't need it due to the Pi's internal clock, but if I do it's here if not I got a tool for a future project)
http://www.ebay.com/itm/301141108103?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649
CO2 and hazardous gas sensor to monitor rocket mass stove output and "plant oxygen"
http://www.ebay.com/itm/271340980895?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649
A day light sensor to measure amount of sunlight and also help regulate the heating an cooling system ie; fan off in summer heat, or heater on at dusk, basically a buffer between my temperature sensor thermostat http://www.ebay.com/itm/310828123345?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649
A Barometer just cause I am already monitoring other enviromental factors and if pressure drops suddenly we most likely gonna get rain. http://www.ebay.com/itm/371043374165?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649
Temp and humidity sensors for compare and contrast of temps and moisture. Also thermostat controls.
http://www.ebay.com/itm/111238295400?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649
water level sensors for activating a reserve (rain water tank) to add water if fish tank level drops to low.
http://www.ebay.com/itm/360902277336?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649
A mega cause I figure I am going to have this baby loaded down with I/O ( you guys tell me if I need more than this mega, Arduino is open source so this isn't pirated board, right?)
http://www.ebay.com/itm/251427905210?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649
and I am building this with a buffer chip just cause I think it may help with expansion in the future, and it's a little more modest (so I'll tackle it while I am reading about PI and Arduino code.)
http://www.instructables.com/id/The-Raspberry-Pi-Arduino-Connection/step1/Parts-needed/

I haven't bought relays boards because, I haven't decided on what voltage I want some of the new hardware to be.

Oh and I will be working on a "sketch" soon, I hope.

@wildbill I plan on having the Pi hooked to my WiFi network. The Arduino and sensors are close enough to where my Pi will broadcast. That I probably won't have a cable running longer than 5foot (1.5meters)
The green house is 8x12feet, with a 300+gallon (1100+litre) tank, but all my sensors can be confined to a very small portion of this area, and Network to the outside world via WiFi.

i have created a project that appears to do everything you want and it uses only an Arduino Mega. i can log data, and adding additional sensors and/or logic would be very easy. you can see it here if you have not seen it

http://forum.arduino.cc/index.php?PHPSESSID=ddgk1tp7vb4186vkhudm22c8p6&topic=140740.0

/subscribing as I am interested in your project. I want to build something similar when I have some time, but with a PCDuino instead of a Pi - purely cause I have a PCDuino and not a Rasberry Pi. As my "sensor hub" I'm planning on using an Arduino Leonardo (again, what I have at hand) or perhaps even a "bare bones arduino". For communications I might be looking at using I2C, or perhaps purchase a couple of 433Mhhz radios - they're much cheaper than bluetooth / wifi.