Experiment: what causes algae, the rotting plant hypothesis

Tom Barr

Staff member
Jan 23, 2005
The rotting plant hypothesis has been around for sometime.

We all agree on a universal observation that if the plants are not doing well, not growing well etc, this can lead to algae, when they do well, generally, the tank does very well, no algae. This same observation is true in natural systems also.
When plants rot/decay, they tend to produce quite a few compounds. These compounds produced after the plant tissue dies, and/or the secondary effects of lower O2, bacterial blooms/population increases that attack the dead plant material, may play a role.

Similar to a control test with allelopathy, using activated carbon in a large amount while placing the a defined amount of dead aquatic plant material to a known aquarium volume, may offer a simple test methods.
The activated carbon(AC) would be a wide range of molecule sizes to remove a wide range of chemicals. This treatment would serve as a control, while the non AC treated tanks would be the experimental treatments(say different amounts of decayed or dead aquatic plant material)

Observations would be algae and plant health for each treatment, we could use glass slides to measure the amount of algae that attaches per unit time per treatment but this requires more resources than most hobbyists have.
Still, if there are obvious differences, this might be a fairly simple approach.

The rotting of Rotala macrandra vs say Bolbitus likely would be different also, but the softer fluffy type stem plants likely could eb grouped together.

We note in well planted stem tanks that when the CO2 goes off line or some other factor that causes the plants to lose leaves, melt etc, we often have trouble and algae.
Generalizing that poor plant growth = algae bloom, there might be something to this.

So how to make a "standard" poor plant health treatment to an otherwise stable healthy system becomes a method issue. This way light/CO2/nutrients/filtration etc are independent.