Start is part of the basic 4 and is required. This is part of the carbon food source for the bac. It is considered one of the key elements of ZEOVIT.

It is recommended:
ZeoLith (rock) 1L per 200 to 400 litres of net tank volume
ZeoBac 1 drop per 25G daily for first 2 weeks after a Zeolith change. 1 Drop per 25G every 2 to 3 days after
ZeoFood Same as ZeoBac
ZeoStart2 2ml per 250G (1/2 in the morning and 1/2 at night)

All other Zeo products considered supplements

... Dude, who's selling you your Zeovit???

Edit: Nevermind, that. Anyway, make sure you read over the proper guide for Zeovit, which can be found here:

http://zeovit.com/forums/showthread.php?t=10354

Important stuff there!