The nitrifying bacteria in a tank form a colony. This is comprised is many individuals. In an established tank with a fairly consistent bio-load, the amount of ammonia being created is fairly stable. As we cycle a tank the bacteria will multiply when there is more ammonia or nitrite than the colony requires to thrive. If we add things that increase the ammonia (and thus the nitrite) levels, the bacteria respond by reproducing. They will do so until their capacity to process ammonia/nitrite is equal to how much of these things are available.
It is important to realize that in an established tank the colony itself is stable, however individuals are dying every day and others are multiplying. The individuals change but the colony as a whole does not.
In an established tank, you will have the appropriate number of individuals to keep a stable colony. But what happen if ammonia or oxygen is suddenly lacking? The bacteria can sense this and they will respond by going dormant. When the messing items return, the bacteria wake up and get back to work/ However, whether they resume at the level they left off at when they went dormant or they have degraded their numbers depends on two things. What shape they were in when they went dormant and them how long they remained that way. What this means it if you remove 100% of the fish, there will be no more ammonia or nitrite being produces for the mot part, and they will go to sleep.
On the other hand, if you remove only half of the fish from the tank, the result is less ammonia and that will cause the individuals why natural die each day are not going to be replaced. The result is the colony size will shrink its numbers until it is in balance with the available ammonia levels.
So, had you removed all of the fish from the system a month ago, what you would have today is almost 100% of the bacteria you had when most of the fish were removed. However, by removing most of the fish what you have today is a colony that has shrunk to match the supply of ammonia your few fish now create. You are, in effect, back into a fish in cycle when it comes to adding fish. Do not just restock to the prior level, you must add new fish gradually to avoid ammonia and nitrite spikes.
If you have live plants, this changes things some as they process ammonium. You need to be testing regularly because you may see ammonia showing up and if you do, test for nitrite as well. Given such a big tank and so few new fish, it will take some time for ammonia to show up. Please hold off on the ray if you can until you know the tank is safe to add it. This could take a bit of time. You will know if you keep testing for ammonia daily for at least a week or more. The water volume may be enough to protect you, the daily testing will confirm this.
You can do no harm if you wait for longer than needed to add more fish, you can do harm if you add them too soon. Patience is the most difficult skill we as fish keepers need to learn.
