I think that was an excellent decision to change your plans and upgrade from a 24-gallon nano cube to a more substantial 46-gallon aquarium. Bigger (hence more stable) and taller is generally always better when considering a seahorse setup.
The size and the location of the tank are the first things you must consider when preparing an aquarium for seahorses. Unless you will be keeping one of the miniature breeds of farm-raised seahorses, such as Hippocampus zosterae, H. breviceps, or H. tuberculatus, it’s best to start with the largest aquarium you can reasonably afford and maintain (the taller, the better). In general, a tank of at least 40 gallons (150 L) is preferable since that’s the size when one begins to see significant benefits in terms of the greater stability a larger volume of water can provide. An aquarium of 40-gallons or more will be more resistant to overcrowding and to rapid fluctuations in temperature, pH, and salinity than smaller setups. The larger the aquarium the larger the margin for error it offers the aquarist and the greater the benefits it provides in terms of stability.
It is equally desirable to select an aquarium at least 20-inches high when keeping the greater seahorses. They need the vertical swimming space to perform their complex mating ritual and successfully complete the egg transfer, which is accomplished while the pair is rising through the water column or drifting slowly downwards from the apex of their rise. If the aquarium is too shallow, eggs will be spilled during the transfer from the female to the male’s brood pouch, and mating becomes increasingly difficult or impossible below a certain minimum depth. A tall aquarium can also help protect the seahorses from depth-related health problems such as bloated pouch and certain forms of Gas Bubble Disease.
Obviously, either one of your 46-gallon aquariums should work well with your seahorses. All other things being equal, I would generally opt for the tallest aquarium in a case like this, preferring the added protection the extra water depth provides from gas emboli and the various forms of GBD. So providing you can work comfortably in an aquarium 30-inches tall, without skimping on maintenance because the tank is awkward to service, I would be inclined to go with the taller tank that was only 20 inches wide. That should work well if you’re willing to limit yourself to a modest herd of seahorses.
Although height and therefore water depth is a priority for seahorses, good bottom space is also desirable for their various social interactions and behaviors. The roomier the aquarium, the more active the seahorses are likely to be in terms of swimming and exploring their surroundings. The 36-inch long aquarium that is 21-inches high could also make a successful seahorse tank, if you feel the taller version would be too cumbersome to service and maintain. Otherwise, go for the added height!
If you haven’t already seen them, there have been a few other threads on the Ocean Rider Club discussion board at seahorse.com from hobbyists who were just starting out with seahorses that you should also find to be of interest. They discuss setting up an ideal system for seahorses, filtration, feeding, lighting, circulation and so on. I’ve provided links to those discussions for you below, so please check them out. I think they will answer many of your questions about keeping seahorses:
Click here: Seahorse.com – Seahorse, Sea Life, Marine Life, Aquafarm Sales, Feeds and Accessories – Re:ok stocking density…
Re:Hello, newbie here! – O http://www.seahorse.com/option,com_simpleboard/Itemid,144/func,view/id,1004/catid,2/
Click here: Seahorse.com – Seahorse, Sea Life, Marine Life, Aquafarm Sales, Feeds and Accessories – Re:Setting up a 100gal for
Re: Guidance on Keeping Seahorses:
Re: New to seahorses and I have lots of questions!
Re: Tank set-up advice
Re:New-comer in need of help
Re:New with lots of questions 🙂
Best of luck with your new seahorse system!