Hi Billie,
Thanks for the quick reply 
Is the pH Meter all the time into the water to measure the pH?
I had some information which sad that letting the ph probe all the time in the liquid will cause damage?
Perhaps this is wrong I only want to confirm it.
And second question : basically I only need one ph Probe and two peristaltic Pumps to setup a pH measure and adjustment station?
I have a Arduino UNO Board with max. 5V on the Digital Output with max. 30mA
I have found those two things now: http://www.aliexpress.com/item/Free-shipping-6V-DC-DIY-Dosing-pump-Peristaltic-dosing-Head-For-Aquarium-Lab-Analytical-water/1003369174.html
http://www.aliexpress.com/item/PH-Electrode-Probe-BNC-Connector-for-Aquarium-PH-Controller-Meter-Sensor-NI5L/938643629.html
Do I can connect them directly to the board or do I need a extra power supply ?
And as I have rad you divided the code so I can just take the part that fits?
And last but not least 
: Why do you use a DC 9V plug for your arduino ? I thought 5V is max
Greetings
BillieBricks:
Hello Tonno,Reading the pH is fairly simple as the Phidgets 1130 outputs an analog signal which can be converted to a pH. You just do an anologRead on the pin which connects to the Phidgets and run this calculation --> 0.0178 * sensorValue - 1.889
What outputs is the current pH value at a constant temperature of 25°C...Dosing is not that easy. I work with a Setpoint and a Hysteris. The setpoint is the pH I would like to have and the hysteris is the amount the pH can deviate from this point.
Explaining how the code works is not that simple, but here goes...
I first check if the pH is above or below the setpoint. Then change a variable according to that so the program knows if it's a base or acid that needs to be added. Note: If your plants are healthy and absorbing nutrients the pH can only go up. That's because plants use the negative ions for nutrient absorption...
Let's assume the pH is above the setpoint. The program now checks if the pH is above the hysteris. If so, dosing will start (which is a small peristaltic pump) until the pH reaches the setpoint. If the setpoint is reached then dosing will stop and the variable is set to 0 again.
This repeats constantly...I hope this helps
