CJG
These will answer most of you questions from your first post
Ozone and the Reef Aquarium, Part 1: Chemistry and Biochemistry
http://reefkeeping.com/issues/2006-03/rhf/index.php
Ozone and the Reef Aquarium, Part 2: Equipment and Safety
http://reefkeeping.com/issues/2006-04/rhf/index.php
Ozone and the Reef Aquarium, Part 3: Changes in a Reef Aquarium upon Initiating Ozone
http://reefkeeping.com/issues/2006-05/rhf/index.php
Some notes;
It destroys the nitrate ion
I has no effect on Nitrate. It actually destroys Ammonia to a degree and converts NO2- to NO3-. Nitrate is in a very stable state where it can not be oxidized anymore by Ozone or reduced by Ozone. There is no means where N can leave O3 form the Nitrate ion with Ozone.
ozone is good at killing everything
Only if it is high enough, contact time 30 sec or more and ORP @ 700 mV or higher. At ~ 300 -400 mV you will get a reduction of bacteria in the water column by about 10%. It will have zero effect on any parasites. 30 secs or more is where 100 % is killed if at 800 mV.
have a bag of carbon at the exit point of the skimmer to remove excess O3 which in high amounts will kill fish
In seawater rarely is this the case as the half-life of Ozone is only a few seconds. Most of what happens is the Ozone converts Bromide to Bromine or Bromate ( from a second ozidation). It is these that the carbon is used to remove form the system. It is also these that can kill fish or to high of a REDOX. In system without Bromide then you can have excessive Ozone. If the Ozone is to high then the Chloride ion gets converted to Chlorine, which can also kill fish, where carbon will also convert the Chlorine back to Chloride, just like the carbon converts the Bromine back to Bromide. If there is any unbound Ammonia or certain Ammonia base moelcules then there may also be the the conversion to some Broamine. In unbromided systems, such as some public aquariums where there is no Bormide in the sea mix, then degassing towers are use. These are really nothing more than big trickle filters. As ozonated water comes down high velocity / vol air its blown up, which drives the Ozone out of the seawater and into the air. The air is then vented to the outside.
you will get more efficiency of the ozone if you hook it up to a skimmer.
You will get less if it is hooked up to a skimmer vs. a Ozone reactor. Skimmers are all venting Ozone out through the skimmer cut, where as reactor do not but drive the Ozone into the water under pressure in a sealed cylinder.
Here are some examples of reactors and the article posted above has very cost effect reactor made out of coiled tubing.
http://www.reeffrontiers.com/forums/showthread.php?t=38219&highlight=reactors
As far as a means of reusing water and what to do with it follow Don's advice. He has spent allot of time at this and know all the ins and outs.