Once again I am suprised by the l the misinformation in this thread.
1. The nitrite oxidizers in Aquariums are not nitrobacteria they are Nitrospira. The former thrive on high nitrite levers and the latter on lower.
2. Neither Fritz nor API contain Nitrospira. The only proc=ducts that do are Dr. Tim's One and Only and tetra Safe Start. The reason is simple, nitrospira are protected by a patent.
3. The bacteria in the bottle, if they are the right ones, are not dead. They are dormant. There is a ton of science on this. The nitrifying bacteria do not form spores, they divide. So they need a strategy for surviving bad times and that is they can go dormant. As soon as ammonia etc, is present, they wake up and go back to work.
4. Using the wrong bacteria to start can aid a cycle a bit. What it does is provide food to the other heterotrophic bacteria that also live in the biofilm with the nitrifyers.
5. The things added like Prime and API bacteria did not help. I do not care what the makers claim for these products., If they worked as advertised, you would not be having the issues you report. Prime actually slows cycling it does not speed it up. Why? Because ammonia as NH3 is what the bacteria need to reproduce and make a tank cycled. Prime turns it into something the bacteria cannot use with the same efficiency. The best dechlor to use during cycling is one which DOES NOT CLAIM TO DETOXIFY AMMONIA. Ammonia as NH3 is what drives the cycle.
For the curious when the research was being done into the exact bacteria in tanks and then to creating a starter bacteria solution, they actually tested the Fritz product at the same time. The result was it did not accelerate the cycle and when the cycle was established, the Nitrobacter from Fritz was basically not there, it had been replaced by Nitrospira.
There is a ton of science out there on all of this. There is also a ton of anecdotal information out there which is not really accurate.
First. please read this article here on how to help your fish and fix the problem: Rescuing a Fish-in cycle gone wild Part II
Next, how exactly did you cycled the tank? 6 weeks should be enough to cycle most tanks so they can be fully stocked. And the way you know it is done right is that you add ammonia between 2 and 3 ppm and in 24 hours you have 0 ammonia, 0 nitrite and (with no live plants in the tank) some level of nitrate.
When I ask how I would want to know your tap water params, what ammonia you used and some of your test results along the way, i would like to see info re water changes if you did them during the cycle and why.
edited to fix the link so it doesn't have a smiley face which makes it not work