After i didn't found a solution for
i tried to use tierprices with a amount of 1 or upper... now it says
Fatal error: Call to undefined method Mage_Catalog_Model_Product_Type_Price::getGroupPrice() in /var/www/clients/client1/web1/web/app/code/core/Mage/Catalog/Model/Product.php on line 639
on product view (if i'm logged in in the group of the tierprice). As long as the error is in a core file it couldn't be the template.