The fruit of the alder trees (alnus glutinosa and alnus incana) has been widely known in Europe for aquaristic use. Especially betta and shrimp breeders make use of the acid tannin which the alder cones release to the tank water. As tests have shown, a single cone already will tint the water brown which indicates the humid acids.
Dosage of Alder Cones
The tanning agents effect the pH value and will lower it – the exact scale depends on the number and quality of cones, and on the carbonate hardness of the water.
It is also possible to make an infusion with boiled water and only add the cold extract without cones later.
Admittedly, the quality of alder cones differs as it is a natural product, and the percentage of tannin can vary. So, if you bought cheap stuff, they might not have great effect on the pH. Be careful with overdosing, as shrimp need time to adapt! Take your time and do not throw all cones into the tank at once. I recommend to always run a test. Dosage Examples vary from
- 4 alder cones on 1000 ml (1 L) water lowered the pH from 7.0 to 6.4
- 1 alder cone for 10 L water
Effects and Benefits of Alder Cones
In a lower pH, the bacterial density also is low, which can help prevent bacterial infections and hatch shrimp eggs properly. Besides, fungi also grow worse in an acid surrounding. So, we have this reaction chain:
- the alder cones release humid acids to the water
- the humid acids will lower the hardness and therefore the pH
- a lower pH reduces the density of bacteria and fungi (it is supposed that acids can pass cell membranes of bacteria easier in a pH ~6 and effect their duplicating and growths)
However, the water will have an obvious brown tint. If you clear it up with Seachem Purigen or charcoal, do not forget that you remove the tannin and take back the positive pH effect!
From our observation, especially shrimp like to feed on alder cones – and baby shrimp have a good place to sit and hide. We remove the cones after 3-4 weeks, before they decompose and break apart.