Hey,
I'm not in Erlangen, but all the way to the south in Konstanz. If You drop by, I'd be happy to take You to one of the local pools or the lake.
Pool Staff in germany have a reputation of being very strong minded in their regime. It's a cliché, but I found it partly true. (Ask Your locals about the 'Bademeister' ;-)
Usually, Fins are not tolerated in public pools except for certain hours, when diving- or rescue clubs have their training hours, but this might not be the case around Erlangen.
You could browse for local diving clubs. (Keywords: 'Tauchen' 'Club' 'Tauchclub' 'Verein' - don't know how good Your german is
or the DLRG, the "Deutsche Lebensrettungsgesellschaft" - The 'German life-saving-society' which is a water-rescue club, mostly.
The local DLRG have regular training hours once a week in one of our pools and seem to be fairly open for guests, but I can't say for sure, because I have never been to one of their trainings. Next week I'll go see them.
So, what I can tell You is: Your mileage may vary. I'd say take the fin
, You'd be Biting Your Ass (as we german's say ;-) if you found some place to dive and not had them with You.
Greetings from Lake Constance,
sanso