If one needs to dilute tank water in order to get a "real" nitrite reading it should not be done with tap water. It should be done with either ro/di water or else with distilled water. Tap water often contains things that will affect the reading.
This test kit problem is one of the biggest issues when doing a fishless cycle. The max. level that nitrite should reach reads roughly 16.5 ppm on an API kit. Using one's tap to dilute a water sample will be an issue as one gets near that 16.5 level. A small amount of stuff in tap water can change the results. If it is changing them from 8 ppm to 9 ppm that isn't a problem. That same 1 ppm going from 16 to 17 is.
Next, when doing a dilution one needs to measure accurately. A measuring error of only .25 ml in each water sample doing a 50/50 test changes things by 5% or so. 5% of 16.5 = .82. Considering things start to stall at about 16.5, not much room for error. And then when you may be doing a 1-3 dilution the possibility for error starts to magnify greatly.
Once nitrite gets over 5 ppm on that API kit, only one thing really matters, not letting it cross above 16 ppm. It needs to stop rising and turn back down or the problems start. But the way to control nitrite is by controlling ammonia.
There is a little chemistry involved which may help to show this. If we put 1 ppm of ammonia into a tank as measured on an API kit, and if there were ammonia oxidizing bacteria but no nitrite oxidizers what happens to that ammonia? It becomes 2.8 ppm of nitrite on the API kit. So if you put in 4 ppm of ammonia, it will become 11.2 ppm of nitrite. Add another 4 ppm dose of ammonia and the foundation for creating 22+ ppm of nitrite is there. But that is an over simplification. The ammonia is not converted all in one shot, it takes a number of days during the start of a cycle. In addition, even with almost no nitrite eaters present to start, there will be be reproduction which accelerates with time. So even though we can see how much nitrite could result, it should always less than this due to the nitrite oxidizers reproducing along the way as the nitrite builds up.
The repeated addition of ammonia on a frequent basis can easily push nitrite levels out of control and kill a cycle. So we have two options. The harder one to handle is the diluted test method due to the things mentioned. The other approach is to lower the amount and frequency of ammonia dosing which heads off the problem before it can begin.
A great way to to avoid the problem entirely is to seed a tank with a good helping of bacteria from an established tank or by using one of the few good bacterial additives. Either gives a jump start to the nitrite oxidizing bacteria. In the absence of such a bacterial jump start, it is best not to exceed 3 ppm of ammonia and to use this somewhat sparingly. That way it simply doesn't matter if the nitrite kit can measure it since it should not be possible for it to become an issue.
Circling back to the OP's situation I advise you to stop adding ammonia and to watch nitrite until you know it is moving down. Not just a dribble down but a clear no-bones-about it drop. Once you see it under 10 ppm and dropping, you can add 1/4 of your original ammonia dosing amount every 3 days to keep the ammonia bacs happy. They will not starve. When you test and see two things: .25 ppm or less of ammonia and you clearly see the nitrite being under 1 ppm, dose 3/4 of the original ammonia amount, wait overnight and test- 0/0 means you are cycled. .25/0 would also likely indicate you are cycled but getting a false ammonia reading. To be sure I stated it clearly- the 1/4 and 3/4 amounts are based on what ever volume of ammonia you used in your very first addition to get the ammonia to 4 ppm.
At this stage, with no living things in the tank, the nitrate is not a big issue. However, if you do a water change you will not only bring the nitrate down, but you will also lower the nitrite which should get you cycled faster from where you are now.
....... and addictive.
