Hello Joesi,
This '+' stock is overstock limit, which will be used as stock when current stock is not available. If you want to set this all as 0, you can set current stock and overstock limit 0. This will solve the issue with 0 stock products. To publish the current stock and overstock limit options Go to Sellacious backend > Settings > Global Configuration. In "Backend Display Options" select "Over Stock Limit" for the desired product type.
I hope this helps.
Thank You
-Team Sellacious