[bob_the_fish]

I have heard that some fish farmers use hydrogen peroxide as an emergency source of oxygen i.e. if pumps fail etc. a measured amount is added to the tank and this keeps the dissolved oxygen levels up. I have tried this - pretty empirically - and have found that the speed of the reaction varies tremendously. Can anyone think of why the water being freshwater or seawater would make any difference and also, if there is more organic matter in the water, should this speed up or slow down the breakdown of h2o2?

 

[Yggdrasil]

The breakdown of hydrogen peroxide can be fairly slow in some cases.  However, there are many things which can speed up or catalyze the conversion of hydrogen peroxide to water and oxygen.  For example, temperature will play a big role.  Sunlight can also promote the breakdown of hydrogen peroxide.  Some inorganic salts can catalyze the reaction (e.g. manganese dioxide).  Biological catalysts (e.g. the enzyme catalase) can also speed this process.

[Bakegaku]

The amount of organic matter would almost definitely have an effect.  I noticed from cleaning out water pools for my pets that hydrogen peroxide especially foams up when in contact with algae.