visit
seahorse.org to learn a lot more than what the books will tell you.
Don't use wood or gravel.
Use live sand, live rock, and macro---macro is great. They prefer branchy LR, such as tonga branch and others.
(FYI: the tank is too large for dwarf seahorses who cannot be kept with LR/LS unless it is hydroid-free anyways)
Parameters: salinity 1.021-1.024, pH 8.1-8.3, ammonia 0, nitrite 0, nitrate preferably less than 20, can get up to 40 but not so good.
Temp varies on species. 20g is kinda small for beginners of sh but doable.
Most tropical seahorses get larger and don't thrive in a 20g.
If you could manage to keep the temp under 70*F, you could have a mating pair of H. Capensis do well in there.
You could get 2 pairs of H. Breviceps if you could manage to keep the temps at 65*F since they are a temperate species.
If you would like to have your seahorses mate, they prefer taller tanks with 3-4x the height of the seahorse. Ex: 6" sh breeds well in 18" tall(er) tank
