Hello; Beneficial bacteria (BB). Pages have been posted about them. As far as I know there is not a "for sure" over the counter product you can purchase to get BB.
They can be had for free but there are catches. The simplest way to get a starter culture is to grab some object which has been in an established tank for some time, like months or at least a few weeks. If your local fish shop is decent they might let you have some gravel, snails, used filter floss or something from one of their tanks. If you have a friend with tanks perhaps the same.
The BB are all around us. Start a bare tank filled with water and add a 1/4 cup of ammonia every day or two. Do this for a few weeks and you will have some BB colonies on surfaces in the tank. They show up. This is one method of doing what is called "cycling" a tank. I guess cycling is a made-up name for what happens in nature. Adding ammonia is called "fishless cycling". Some prefer this way as it does not harm fish.
Another way to "cycle" is with "fish in" the tank. The fish excrete waste which contains the ammonia. In a few weeks the BB show up and grow in the tank. Many do not like this way because ammonia harms fish. A way to reduce the harm is to do more WC to keep the ammonia down but that sorta slows the process down.
The goal is to have enough of one sort of BB growing on the tank surfaces to completely convert the ammonia into nitrite. Then to have another sort of BB to convert the nitrite into nitrate. Nitrate is the least toxic of the three and most of us consider keeping nitrate down to 20ppm or so to be good enough. A problem is the BB are slow growers compared to other bacteria. Makes cycling a tank from scratch a week's long thing.
You , the OP, are embarked on a "fish in" way of cycling. I suspect you did not know such. A puzzle is why the ammonia is at zero after the tank is setup since last April. Hence my suggestion to "standard" test the test kit with distilled water.
Let me open another potential can of worms not related to ammonia or cycling. That being your tap water. If you know about prime (SAFE) and use it or some such water conditioner at WC then I will not need to go into that. I am thinking of chloramines or chlorine added to tap water.
