Angie,

The reason most suggest that you do not mix seahorses is because you never know what pathogens you may introduce to the varied species. Most, but not all, are from differing waters. Some ranges overlap. Each fish is susceptible to certain diseases etc. By mixing them, you may, in effect, do what we as a country did to the Native Americans...introduce some virus, bacterium, etc. that they have never been subjected to and "wipe them out".

Now... I say that...but must preface the thought with the following....This was a "rule of thumb" when you could pretty much ONLY get wild caught ponies. Wild caught ponies are more likely to carry these diseases and bacteria on/in them than tank raised fish. I, personally, don't know if this fear is valid with Tank Raised Fish. If truly tank raised, the chances are that NONE of them have been exposed to such threats.

For what it's worth, I have pipe fish (wild caught) in my tank with my ponies. I QT'd them for a month+ before introducing them. Also, I have a sneaking suspicion that ONE of my males is not a true 100% Reidi. I think it may be a "hybrid"...which...brings me to my last point...

Hybrids are just that..a mix between differing species. While some believe that the hybrids are more hearty, and robust, others (purists) cringe at the thought of a mixed breeding. And, from a scientific point, with good reason. Keep in mind that if you do have Reidi and Erectus in a single system, there is a good chance that they will interbreed. YOU decide if that is something you want to deal with. I don't think it's a true "bad thing" in the hobbyist community as long as you let other possible recipients of the fish know that they are hybrid. Otherwise, if you want to keep the "lineage" of your fish going, I'd not let them interbreed.

Dave