Can the Arduino store data over time? For example, can it give data on the pH, temp, etc for the past 30, 40, 60 days? Maybe presented in a graph, or at least a table?
I'd assume you'd be able to write data to the sd card and store them in files. my idea with this stuff would, since i'm a web guy, interface with a website and store the data in a database.
not having any experience with arduino itself, i can only assume that with a wifi connection one would be able to make requests to a website for that data for reading/writing purposes.
The Arduino itself cannot store a large amount of data over time. You can have it store required data on an SD card so it can do data logging.
For interfacing with a website, the same idea can be done, but it would have to access the site every x seconds/minutes that you are measuring the data (i.e. you might want to measure temperature or pH more than once an hour...I have mine set for every 5 minutes).