Ph, ammonia, nitrite, and nitrate probes

Im trying to make an automated fish tank and my biggest problem is that i cannot find the right sensors to measure the nitrite, nitrate, ammonia, and PH of the water. i have found a few ph sensors i can use but i still need the guidance for making it work with the arduino. any help would be greatly appreciated.
-Bogart21

It depends on the sensor and how it "reports" the reading. links would help us help you!

Mark