When you are ready to purchase your first aquarium, one of the first things you learn is how to properly cycle the aquarium and how to slowly introduce new fish to avoid ammonia spikes while the colonies of beneficial bacteria are developing. That's easy enough to follow -- but what about when you have to move an existing community of fish to a new home? Maybe you moved and have to re-establish the aquarium, maybe you're moving to a larger or even a smaller tank; whatever the reason, there are ways to safely move the fish without as much risk of ammonia spikes.
A properly cycled tank contains a healthy colony of bacteria that breaks down ammonia from a fish's waste and uneaten food into nitrites and then into nitrates. In a healthy tank, there should be 0 ammonia, 0 nitrites and less than 40ppm nitrates (20ppm if you have invertebrates such as snails or shrimp). Without sufficient amounts of beneficial bacteria, ammonia and nitrite in the water may be fatal to fish.
Beneficial bacteria live all through the water and on every underwater surface in the aquarium, but the water itself carries a very low concentration of bacteria so it's not very effective to simply transfer water from the old aquarium to the new in order to maintain bacteria levels. Ideally, you will be able to transfer some old filter media to the new aquarium, or even a handful of gravel or fake plants that will all have beneficial bacteria on them. Make sure that the materials of your choice stay wet with tank water until they can be placed in the new aquarium.
Alternatively, if you have EcoBio-Stone products in your aquarium, that will be sufficient to switch over to the new one. EcoBio-Block has a lot of beneficial bacteria living in its volcanic rock and has quite a bit of surface area so a lot of additional bacteria get transferred over from the established tank. It is not necessary to keep EcoBio-Block wet, but it may help eliminate any minor ammonia spikes that may occur after the transfer as there will be more active bacteria immediately if kept wet. EcoBio-Block will also allow you to wait a little bit longer before doing the first water change as it provides essential minerals that would otherwise have to be replenished through water changes, giving the fish extra time to de-stress after a big move without being bothered.
Make sure not to put whatever bacteria-containing materials you've chosen into the new aquarium until a de-chlorinator has been used in the water as chlorine will kill the bacteria. Keep close tabs on the water parameters for the first week after the transfer, doing minor water changes as needed to compensate for any ammonia in the system that may not be compensated for by the bacteria yet. Watch the fish closely for any clamped fins or red, puffy gills as these may be signs that the water parameters are off. If these simple guidelines are followed your fish should have a relatively effortless and healthy move.