Henry, thanks for your reply.
The pipefish i have, a Doryrhamphus melanopleura according to your article and a D. excisus according to the books i have, lived together with 2 mandarins in a 260liter tank. They had plenty of food collecting from the 'live rock'. They rarely accepted frozen food like artemia because of the 3 Apogon leptacantus.
Unfortunately,1 mandarin died because a Fu Manchu died and posioned the tank, i guess. The second looked bad and transferred it to the reeftank in the living room where i'll probably will not see her (they were both females) because it is packed with fish but plenty of food from the rock. In that tank is also another dragonet, here we call them the LSD-dragonet, and that want has a big belly.
Paul