Seahorse stocking capacity 20 extra tall

[rayjay]

While occasionally people have been successful with smaller tanks, it does take a heck of a lot of extra husbandry to work compared to the recommended tanks.
For normal sized seahorses like reidi and erectus, the recommendation is 29g/30g for the first pair, and fifteen extra gallons for each additional pair.
Keeping the water clean enough is a big challenge for long term survival of most seahorses as they succumb first to bacterial infestations, and secondly to parasitic pathogens introduced to them by other fish they get exposed to. (unless those other fish are from the same breeding source)