Andy, whats the problem with the Jebao, and what are you guys adding by default (minimum needed)?
Nothings wrong with it, it's inexpensive and does the job, it's just the quality control is not very good (e.g. mine came from the factory with the dosing heads fitted the wrong way round and one of the buttons has to be pressed really hard to make it work). Once the dosing heads are in the right way round it does work, you just have to keep on top of calibration.
The minimum a Jebao can dose is 1ml, so if you want to dose smaller amounts you need to dilute your 2/3/4 part (or set it to only dose every 3 days or whatever).
I've only got a few frags in mine so I'm just dosing by hand at the moment.