The First Two Weeks
The first two weeks are the most crucial. The nursery should be a simple setup, and not too large. Be careful about what airstones you use. If the bubbles are too small, the fry will consume them, thinking they are a meal, and die. If you use a good circulation system you may not need extra aeration. A bubble-up or sponge filter and a small power filter should suffice.
If you chose to add a substrate or gravel, stick to dolomite, aragonite or crushed oyster shell. This substrate type will buffer the pH of the water and help keep toxins down (if the gravel is already biologically established). Some aquarists say that gravel is not a good idea because it makes cleaning a little more difficult.
Ammonia and nitrites should be at or close to nil, and nitrates at less than 10 ppm. Like most marine species, a pH of 8.0-8.3 is ideal and a specific gravity of 1.020-1.024. Know what temperature your species perfers since it can range anywhere from the low-60s to mid-70s (Fahrenheit). Maintain your water quality in the nursery by doing frequent partial water changes, about 25-30 percent every week or so. To save money, you can use this old water for raising the brine shirmp.
If you have live rock in the tank, make absolutely sure that no bristle worms and crustaceans are inside. They'll eat the fry. The baby seahorses need many hitching posts, so make sure to have some holdfasts available in your tank. The precarious status of seahorses in nature due to a rapid decline in the quality of their native environments has made breeding them a labor of love for the conservation-minded Hippocampus fan.