Clare,
I will explain the best I can, but Marty would be the best source here as all I will really be doing is restating what he has shared with me (and the rest of the board).
Seahorses have enzymes that are supposed to operate at a set rate. If the enzyme operates to fast, or to slow, it will cause a build up of CO2 gas, which then presents itself as GBD. A seahorse that is predisposed to GBD is one who's enzyme regulates at the wrong pace.
The enyme is called carbonic anhydrase.
Marty is not sure yet if the high level of CO2 causes the enzyme to malfunction, or the high level of CO2 is the cause of the enzyme malfunctioning. Or both in different cases.
Also the predisposition seems to be genetic and carry vary from batches of fry from the same parents.
Also there is a thing called a microprobe which will identify all of the chemicals in the bubble. Kinda of like a gas chromagraph would to a solid substance (Sorry Jefferey Deaver Lincoln Rythme Fan.). When someone has the money to use a microprobe on a gas bubble we will have a much better idea of all of the gases in the bubble, so it will be easier to determin the cause.
Marty thinks for good reason I believe that it is more then just CO2 in the bubble.
Does that make sense?
Rich,
I think much of the misunderstanding you have about GBD is stemming from the idea that it is bacterial. It is most certainly 100% not bacterial.
It does not mimick any bacteria behavior.
There are no reported cases of it being observed in the ocean. It is only something that is observed in aquariums under 4' tall so it has to be part of our setups that is causing it.
Moving a seahorse to a different environment can completely cure the problem, this would not be true if it were bacterial.
GBD does not respond to antibiotics. It is treated with a drug called Diamox which is prescribed to humans to control fluid secretion levels.
GBD in no way mimicks any type of bacteria infection in seahorses that I have ever seen except that if it is untreated it can cause death. (IMO appetite is only affected by the inability to catch the food, if food is available the seahorse will eat)
GBD is most certainly a disorder in where a seahorse has a problem regulating it's CO2 retention on a cellular level.
Myco presents itself completely differently. Not even similiar IMO. I cannot see how the two could be confused.
I do agree with you that many seahorse diseases come from dirty tanks and bad conditions, but IMHO and IME most of these bad conditions are temperature related. Protein skimmers are great at removing a lot of things from the water, but the fact that they remove bacteria does little for the tank IMO. The tank is going to be full of bacteria no matter what. Infact if they removed all of the bacteria, the seahorses would die. Protein skimmers are great in sumps, like I said in my first post in this thread, I use one. Truthfully since I started using it my macro has suffered.
I have a hard time taking much of seahorse.org seriously. Theres just so much misinformation. (related to this, and just in general.) People seem to see one anectdotal thing, and assume causation. Correlation without causation is very common.
Comments like this are going to get you in a lot of trouble with many people. It should be known to you that my first name is Kevin, and I am a mod on seahorse.org.
Writing an entire site off do to misinformation or poor understandings of certain members is short sighted IMO. If all people who read bad info did this, then anyone who has read any of your posts in this thread would have written off RC. Reefcentral is great site with tons of useful information. Why should Fenner or Shimek be disrespected because you had a misunderstanding about what GBD is? They do not deserve that. ( I sited those two because I have a tremendous amount of respect for them both, just want to be clear. Couldn't think of two finer people who deserve absolute respect.

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Seahorse.org is the same way. There are over 5000 members, but very few great minds. You should know so of the leading and most respected authorities in the world post there . If I know anything, it is only because they took the time to share there thoughts with me and provide me some direction. With members like Dr Martin Belli (Labdoc), Keith Gentry (KG), Marc Lamont (Marc), Diane Baxter (DianeB), Dr Lisa (LisaD), and Dan Underwood (DanU) to name a few, I really feel honored to be a part of that group. I have nothing but the deepest respect for them (both in there knowledge and as people) and can't let a comment like that just float by.
I hope you don't think I am coming down to hard, but realize you just insulted a group of people I hold very dear to my heart.