Pro Shrimp's comment: Alder Cones - very similar to Indian Almond Leaves - release tannins into the water. Acting antibacterial and stress relieving for the inhabitants. Alder cones are very popular with baby shrimp to graze on. Additionally they are a very attractive addition to any tank.

Alder cones can be added straight to the tank where they will be floating for a while until they sink to the ground. To speed this process up you can boil them for a couple of minutes as well. Over time they will slowly degrade and can remain in your tank. 

Benefits

Reduces the risk of bacteria and fungal outbreaks

Provides biofilm grazing for baby shrimp

Relieves stress