Stages of cycle
1. Ammonia usually begins rising by the third day after introducing fish.
2. During this stage Nitrosomonas bacteria oxidize the ammonia, thus eliminating it. However, the by-product of ammonia oxidation is nitrite, which is also highly toxic to fish. Nitrites levels as low as low as 1 mg/l can be lethal to some fish. Nitrite usually begins rising by the end of the first week after introducing fish.
3. In the last stage of the cycle, Nitrobacter bacteria convert the nitrites into nitrates. Nitrates are not highly toxic to fish in low to moderate levels. Routine partial water changes will keep the nitrate levels within the safe range. Established tanks should be tested for nitrates every few months to ensure that levels are not becoming extremely high.
So yes there are NitRATES in an established tank, Nitrites are present in stage two only
In nature nitrates remain very low, generally well below 5 ppm. In freshwater aquariums nitrates should be kept below 50 pm at all times, preferably below 25 ppm. If you are breeding fish, or are battling algae growth, keep nitrates below 10 ppm.
Q: Will adding bacteria solutions, such as those available at pet shops, eliminate the break-in cycle?
A: No, due to lack of an ongoing supply of ammonia and oxygen, the nitrification bacteria cannot survive in a bottle for a prolonged period of time. There are manufacturers making special preparations of the nitrogen fixing bacteria. However, what you see on the shelf at the store is simply the bacteria needed for the first stage of the cycle, not nitritfying bacteria. Since the bacteria needed for the first stage of the cycle is already present in the tank once it is set up, there is no need to purchase more of what you already have.
Clear as mud? Who is the fish keeping professional you speak of? Like what is his actual job?
Bottle bacteria can help get the process started, although I know of noone who was able to completely skip the cycle by using it. I know plenty of folks who have tried.
So your tank will cycle when you start registering Nitrates with 0 Ammonia and 0 Nitrite then you can buy more fish.