Kris is correct, sir — a 50 gallon aquarium is an excellent choice for the larger breeds of seahorses such as Mustangs and Sunbursts (Hippocampus erectus), which are ideal for beginners. However, it’s not a good idea to try to keep the larger species such as H. erectus together with the dwarf species such as Pixies (H. zosterae). Although the Pixies and Mustangs have virtually identical aquarium requirements, their different feeding requirements make it difficult and inadvisable to try to keep the two together.
As Kris explained, it would be impractical and wasteful to attempt to maintain an adequate feeding density of newly-hatched brine shrimp for the Pixies in a 50-gallon aquaria. Even if you could manage the feat, the baby brine shrimp would be an annoying nuisance for the Mustangs. The newly hatched brine shrimp are far too insignificant for the Mustangs to eat and they tend to irritate them by clogging up their tufted gills when the Mustangs breathe.
Pixies are pint-size pigmy ponies — no larger than your thumbnail when fully grown — and they would get lost in a 50-gallon aquarium, meaning that they would be all but unnoticeable in an aquarium that size. You really need a much smaller aquarium to do these miniature marvels justice.
If you are interested in both the Pixies and Mustangs, it’s best to set up separate aquariums for each of them. That’s really not as burdensome as it may sound, since a 2-5 gallon pixie tank can be set up very simply and economically.
There have been a couple of other discussions on the Ocean Rider Club message board regarding Pixies or dwarf seahorses that you might also find to be of interest, so please check out the following links when you have a chance. They will give you a better idea of the type of setup that works best for these prolific little ponies:
Click here: Seahorse.com – Seahorse, Sea Life, Marine Life, Aquafarm Sales, Feeds and Accessories – Re:Setting up my very firs
Click here: Seahorse.com – Seahorse, Sea Life, Marine Life, Aquafarm Sales, Feeds and Accessories – Re:Dwarfs – Ocean Rider Cl
Click here: Seahorse.com – Seahorse, Sea Life, Marine Life, Aquafarm Sales, Feeds and Accessories – Re:pixies – Ocean Rider Cl
Best of luck determining the ideals seahorse setup for your needs and interests, Howard!