Hello there, welcome to the forum!
I see no reason to change water to lower nitrite. Nitrite is the product in the middle of the fishelss cycling, and it is needed to feed the good bacteria. Without nitrite, there will be no nitrate. It is the high nitrate you need to lower, but it won't be necessary until the high nitrate concentration is affecting your water PH.
By the way, there is no need to use water softer either. Messing with water PH or/and hardness will just create more troubles for you.
I also see no reason to use TSS at this stage. You have already built up enough bacteria to feed on ammonia, and you are in the process to getting more bacteria which feed on the nitrite. TSS only works as jump start to allow you to have both types of bacteria from the beginning. Using it now will serve no purpose since you already have both types of bacteria in your tank.
There is some information I need in order to help you.
You have not mentioned the ammonia concentration after you have just added it. Usually it needs at least 2ppm. I would aim for 5~6ppm if you are planning on getting a lot of fish at once. Without knowing the amount of ammonia you added, I can't be sure if it is normal for your ammonia to go down to 0ppm in the matter of hours.
It could be normal if you only added very small amount of ammonia. Anything above 2ppm should take longer than a few hours. The aim is to get rid of all ammonia and to drop it down to 0ppm at the end of the day. Of course the faster the better.
Absolutely do not add fish at this moment. Not while you are still seeing nitrite. Nitrite is more toxic than ammonia. It will kill your fish.
Before I know more information, if I were you I'd continue the fishless cycling by adding at least 2ppm of ammonia every day. Make sure you do not take the ammonia test too soon after adding it. The reading wouldn't be accurate. Let it settle for at least 10 minutes or more before test for it.
Keep it in mind, the fishless cycling isn't done until you get no ammonia nor nitrite readings at the end of every day.
Good luck!
