Okay adding 3 Chromis at this point was a mistake. That is done but in light of getting another 50 lbs. of live rock, I would take the fish out and back to the LFS for credit. I say this because the addition of the rock is going to cause additional ammonia and nitrites that will be very detrimental to these fish. Here is an article about ammonia poisoning in fish. Even though your fish don't die they are being and will be put through this terrible condition. Please don't allow that to happen.
Ammonia poisoning is the single most deadly killer of fish grown in aquariums. Most of the times, Ammonia levels build up just after a new tank is set up. But, Ammonia levels can also go up when the tank "load" or the number of fish in a tank is just too high for the tank capacity.
Dead or decaying materials within the tank cannot be fully cleared away using filtration. They decompose and form poisonous compounds. Ammonia is formed when the excretion of fish in the tank, or any other waste material within the tank starts decaying and decomposing. Decayed food matter and any other decaying organic materials can increase the concentration of Ammonia within a tank. When the nitrogen compounds in the decaying matter is released into the water, the decomposing bacteria will first turn this into Ammonia. When this Ammonia mixes with water, it becomes lethal. Very dangerous to fish, the exact toxicity of Ammonia is also dependent on factors like water salinity, pH, temperature etc. It is usually said that if Ammonia can be detected at all by a testing kit, then the concentration of Ammonia within the water is too high for the fish.
Controlling Ammonia concentration within the tank can first be achieved by cycling your tank. The nitrogen cycle aims at developing a rich colony of beneficial bacteria that will feed on the decomposing and decaying matter and will convert them into useful compounds. Bacteria called as Nitrosomonas consume the Ammonia that gets mixed in water and converts this into Nitrites, which are in turn eaten by Nitrifying bacteria. Thus the Nitrogen assumes a much harmless form. That is why it is necessary to cycle the tank before introducing fish in it. It is in the absence of such bacteria that the Ammonia levels start shooting up in a newly set up tank. These beneficial bacteria only need some organic matter and some time to make a colony.
Ammonia poisoning becomes plausible in mainly 2 scenarios. Firstly, if a tank is not cycled properly, introducing a large number of fish into the new tank will cause the Ammonia concentration to spiral. This is because the new fish will obviously be dumping lots of waste into the new water. In the absence of the beneficial bacteria, the Ammonia will not get converted. Thus the fish will die off sooner rather than later. Secondly, if the population of the fish is too high, the organic wastes they produce will be too much for the beneficial bacteria to convert. In such a situation, the concentration of Ammonia increases steadily till the fish start dying off. Other plausible reasons that can lead to Ammonia levels rising are filter failure, lack of maintenance, over-feeding and use of medications. Sometimes over-enthusiastic beginners will also clean the biological filter media, thus killing the beneficial bacterial colony. When filters are being cleaned, it is important to keep the bacterial colony intact. After cleaning, the bacterial colony will need some time to recover and cope with the demands made by the tank.
There are some common symptoms that are seen in fish suffering from Ammonia poisoning. If the fish starts gasping for air and appear almost always at the surface of the water, or if the fish becomes very lethargic and spends a lot of time simply lying at the bottom of the tank, the fish may be showing signs of Ammonia over-dose. If the fish shows a red streaking on its fins or elsewhere on the body, this too could be indicative of high levels of Ammonia in the water. Loss of appetite is another common symptom. If the gills of the fish become red or purple, Ammonia levels need to be checked immediately.
The best way to reduce Ammonia levels in a tank is through partial water changes. A new aquarium should always be cycled. Any new fish should go only in singles or pairs into the tank. Introducing too many fish at the same time will overload your system. Proper maintenance of filters is also a must to keep Ammonia levels down.
