4-5 ppm is too many usually when you do not have seeding you know is at a needed minimum level for sure. You should have been testing every 2 days after adding the ammonia according to the cycling article here. You look well on your way to cycled though.
You should add the same dose of ammonia again now (except recalculate it using the site ammonia calc for a 450 L tank and for 4 ppm.)
You can now test daily. If you read 5 ppm on your nitrite kit, you will have have to do diluted testing to know exactly where your nitrite really is. You must use distilled or RO/DI water for the dilution. You must measure accurately. I normally tell people to fill a very clean measuring cup 1/2 full with tank water and then add the distilled or RO/DI to fill it the rest of the way. Then test as normal using this water and multiply the result by 2. If this still reads 5, then you need to remove enough water from the measuring cup so only 1/2 cup remains of the 50/50 water. Then fill the cup with distilled or RO/DI and test as normal using this mix. Multiply the test result by 4.
The danger line is at over 16 ppm. That would be a reading of 4 ppm on the second level of diluted testing. At this level change about 30% of the water.
You may add a 1/3 dose of the recalculated ammonia amount every 3 days as long as the nitrite is not over 10 ppm and there has been 0 ammonia for at least two days in a row.
When your ammonia is 0 and nitrite on the straight up test is clearly under 1 ppm, add the recalculated ammonia amount. Ff you can test the next day (under 24 hours) and ammonia and nitrite are both 0, you are cycled. Do a big water change, get the tank to temp and add a full load of fish. Ff they are not 0/0, wait until they are 0 and under 1.0 and dose the same amount again and test the next day. This time you should see 0/0 more than likely.
