That’s an excellent idea, sir! I encourage you to upgrade to the 29-gallon Biocube if you would like to expand your herd and diversify your specimens.
Yes, sir, providing they have compatible temperature and feeding requirements, it’s acceptable to keep seahorses of different species in the same aquarium. Some of the other large, tropical seahorses that would do well with your Hippocampus kuda include H. erectus, H. reidi, H. comes, and H. barbouri. (Genuine Hippocampus histrix seahorses are extremely rare in the pet trade, Charlie, so the specimens being offered as H. histrix are almost certainly H. barbouri instead.)
All of the species mentioned above would do well at the following aquarium parameters:
Temperature = range 72°F-77°F (22°C-25°C), optimum 75°F (24°C).
Specific Gravity = range 1.022 – 1.026, optimum 1.0245
pH = 8.2 – 8.4
Ammonia = 0
Nitrite = 0
Nitrate = 0-20 ppm; optimum 0-10 ppm
However, I don’t think it’s a good idea to try to add a new H. reidi to your 14-gallon Biocube for several weeks while you get the new 29-gallon unit set up, cycled, and fully operational. Your 14-gallon Biocube is already stocked to capacity and then some, so adding another large seahorse that you have not quarantining beforehand is taking quite a risk and could jeopardize your whole herd. Under the circumstances, it’s all too easy to envision a scenario where overcrowding and deteriorating water quality in a 14-gallon tank create a stressful situation that results in health problems.
If you want the Hippocampus reidi, many pet dealers will be happy to hold specimens for a good customer while their client prepares a suitable aquarium, so I would like to see you investigate that possibility rather than jeopardizing the health of your H. kuda by adding a new arrival under marginal conditions that hasn’t been quarantined.
If you are going to diversify and try keeping different seahorse species together, there are a couple of precautions you should observe: (1) it’s often best to obtain the different types of seahorses you will be keeping from the same breeder and (2), as always, it’s important to quarantine the new arrivals carefully before you introduce them to the established herd.
If you contact me off list ([email protected]), I can provide you with detailed information about any or all of the different seahorse species you may be interested in, and hopefully that additional input will help you get started off on the right foot with your plans to diversify your herd in the weeks and months ahead.