The 60cm is a minimum size tank for long term housing ( and decribes a
standard size tank holding 54L - approx 14 US gallons )
There is a dispensation while holding for sale but a single male must have
at least I litre ( about 1/4 US gallon ) of temperature controlled water and
must have some plant or other decor in his container for stress prevention.
Water quality can be inspected and heavy fines can be levied.

Not a bad idea IMO.

Sue
PS My German is poor but I had help from Babelfish LOL.