if you have a 400g tank. and your changing say 70 gallons a week, do you set up your system to replace 10 gallons a day to have the same amount of water change as you had before the drip system was implemented ?
For a 400 gallon tank I would drip 200 gallons a week to start with. Use nitrates to determine what your actual rate needs to be. I change 50% several times a week on my 240 to keep the nitrates under 40PPM.
I'm actually in the planning phases of setting up a drip system, and found a calculator thing. Testing is key but at least it will help you figure out the volume of actual change.