When we talk about having a cycled and established tank, we are really referring to having a tank with a developed and functioning nitrogen cycle within our aquarium. Before you cycle an aquarium for the first time, it would benefit you to better understand how the nitrogen cycle works.
So, now after deciding to set-up your first marine aquarium and having your patients tested to the limit waiting for your tank to become cycled, you are now ready to add your first inhabitants.
Wither you decide to start off by adding your first fish or two, or start by adding your clean-up crew (CUC), can really depend a lot on your personal preferences and potentially any algae you would need to start controlling.
You have to be careful picking out a new fish for your marine aquarium. The last thing you want to happen is to take your new home and it becomes sick due to a disease or something else that you could have identified at the store. There are a few things to watch for that will give you an indication there could potentially be a problem with a fish. These indicators to watch for are both in the appearance of the fish as well as how the fish behaves.
Selecting a healthy fish is not a hard thing to do but it does require patience and restraint. If you are not 100% sure that a fish is healthy , it would likely be best not to buy it. The below are the basic rules of thumb that I follow. Keep in mind, following a process like this can never be 100% safe or 100% accurate, so you should still quarantine new additions before add them to your display tank.
As most people have already learned, the key to any type of successful marine aquarium is to obtain the best water parameters possible and to keep these parameters stable. When referring to marine aquariums, I am speaking of both reef and FOWLR (Fish Only With Live Rock) style aquariums. The reason being is that most of the marine fish that we keep are wild caught and come from (or near) a coral reef and therefore would need the same water parameters as a reef tank if they are to thrive and remain healthy over the long term.
Just like the key to cooking a good tasting meal is to use the good quality ingredients, the key to maintaining good water quality in your marine aquarium starts by using good quality water.