I also have 5 fish my now. So replacing it with 5 new fish will ok right
Hello; This should be OK. The size of the fish might make a difference.
Say if the five old fish were small such as neon tetras and the new fish were larger cichlids, then the balance will be off.
A big fish is likely to make more ammonia waste than a small fish. One large cichlid may well be the equivalent of 40 neon tetras.
1st scenario - If the mass of the five new fish is similar to the mass of the five old fish, then the balance of the bb should match fairly well.
2nd scenario - The mass of the old fish is larger than the mass of the new fish, then the balance of the bb will be off but in a positive manner. Meaning there will be a lot more bb around than actually needed. The bb population will slowly be reduced until it is in balance but there will not be an ammonia spike.
3rd scenario - The mass of the old fish is smaller than the mass of the new fish, then the balance of bb may be off in a negative way. The bb population likely will not be able to convert all the ammonia right away. It will take time for the bb population to reproduce and increase enough to deal with the ammonia. You may get what is called an ammonia spike.
This scenario can happen if a lot of small fish or a very large fish is added to even an old established tank.
All that being said there are still some details not covered. In addition to the size(mass) of fish other things may play a role. Some fish are "messy" eaters. Some fish are sedentary while others are active. These things may not have the same impact as mass, I do not know for sure.
Good luck