OK, sound like you are at the place in the timeline where ammonia starts dropping in under 24 hours and nitrite spikes to 5.0+. If you've been adding ammonia to the 4ppm level each morning, then you might want to keep doing that a bit longer and watch the timing of the ammonia drop. When it gets close to being able to drop 4ppm within 12 hours and then if nitrite has also spiked and you are seeing nitrite=5.0 or 5.0+ each day, then you know you are solidly in the second phase (aka nitrite spike phase etc.)
During that second phase you might want to fine tune a bit by lowering the amount of ammonia you add down to 3ppm or 2ppm. Its not guaranteed but what this sometimes accomplished is to help you see, via your nitrite measurements, that your second population is growing and nitrites are beginning to get processed a bit. (eg. maybe after some days you might see nitrite drop from 5 to 4, and it helps with your patience.)
Explanation: If you were adding 4ppm all along (and its perfectly ok to keep doing that and just trust that way on down the line the nitrites will eventually drop to zero!) then each 24 hours or so, that 4ppm of ammonia gets roughly converted to 10.8ppm of nitrite and added to the nitrite that still not been processed. If your nitrite test only tests in the range of 0 to 5ppm, then each day you will just see 5.0 over and over. It might be that what's really happening in your tank is that your nitrite-oxydizing-bacteria have proceessed 20ppm down to 18ppm, but you are just seeing 5, then 5 again the next day (the so-called "nitrite spike") Make sense?
Sorry I was short on the previous answer, I was thinking of leaving for lunch, but didn't.
~~waterdrop~~
