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Re: Protein skimmers in planted tanks.

Hi John,
I'll try this one. 

Protein skimmers work by producing a fine mist of bubbles either by venturi 
action (using a water pump) or by the use of diffusers that produce a fine 
mist of bubbles (using an air pump). There are different designs that attempt 
to prolong contact time between the water and the bubbles.

The organic mulm (detritus) present in the water column has not decayed to 
ammonia yet, and attaches to the fine bubbles in the skimmer. This forms a 
foam that collect in a cup, in most cases. I'm not sure why the organics are 
drawn to the bubbles, electrical charge perhaps? You are, in effect, removing 
organics before they degrade to ammonia, etc. Much of this is ultimately to 
prevent the production of nitrate, as algae is the bane of all reef keepers, 
and nitrate is a great algae food, and can cover corals and destroy reefs in 
short order.

Protein skimming is not effective in freshwater aquaria, I am guessing here, 
because of the relatively less amount of ions in solution in freshwater as 
opposed to saltwater. I would guess it is the ionic activity in the NA+ and 
CL- of the salt in water that makes skimming effective in salt water.

I would guess (again) that the net effect of protein skimming in fresh water 
would be a higher dissolved O2 content and possibly CO2 off gassing because 
of the increased water turbulence.

I kept reefs for many years, and never really cared to explore the chemical 
whys of skimming. I just know it works.

If you have ever observed an UG filter in saltwater vs freshwater, the same 
airstone seems to give finer bubbles in salt vs freshwater.

Once again, I am happily corrected if anyone knows different.

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