Check out this thread for my input on mixing.
Mixing Species Thread
I have started a thread on another forum and have had some good participation. You can find that info
here Unfortunatley there is not a case there yet where someone has mixed without any fatalities.
As far as treatments are concerned I would recommend prazipro, fenbendazole, and a couple of fresh water dips prophylatically. I would not treat with antibiotics unless there are symptoms. The above treatments are all for parasites and available for sale at Seahorsesource.com
I would increase your QT time to 6 weeks min. If the pipe comes to you infected it can take 45 days for it to show outward symptoms. If it has an outbreak in your system with your other fish you could be asking for some major problems.
but there could be a possibility that the reidi were net pen-raised imports that have been exposed and immune to the pathogens carried by WC pipes.
This is a very big misconception.
First off the most common problem with these maricultured (net pen) is parasites. A syngnathid cannot become immune to parasites.
Secondly the issue with the pathogen carried is one of a bacterial nature. There are many different strains of the bacteria so just because a horse was raised in the ocean does not mean it is immune to all the various forms of bacteria in the ocean. The problem with mixing is that there are so many different strains of the bacteria that even WC horses from the same region can carry different strains and when placed in a small system (read aquarium, much smaller then the ocean) have the potential to infect each other.
A syngnathid will be an asymptomatic carrier for the bacteria, but is never completely immune to it. There is a big difference.
When the seahorse is in a weakend state the bacteria begins to release proteins that cause the illness. The bacteria a seahorse has carried for years without ever showing any signs of disease is quite capable of killing it.
For some various reasons mixing syngnathids is more dangerous then mixing other types of fish. I think that the more we begin to understand the mixing issues as well as the temperature issues the more we will be able to see succsessful long term keepers.
I mix WC fish and corals with my seahorses and have never had a disease issue.