# Cycling new tank with old filter



## CoffeeMan

I want to transfer all my fish from my old tank to a new uncycled tank. The new tank has all new substrate, plants, ect... my question is how long until the new tank is cycled if I put the filter from my old tank into the new tank? 

Or would rinsing out the filter media from the old tank's filter be enough to get the new tank quickly cycled?


----------



## Byron

Two different but related issues here. First on the bacteria.

Nitrosomonas and nitrospira bacteria require "food" in the form of ammonia and nitrite respectively. When bacteria that have colonized filter media, wood, rock, substrate, plants, decor--any hard surface in fact--are transferred to a "new" tank, they can last several hours before they will die off if there is no source of ammonia such as from fish. Nitrosomonas bacteria at optimum temperature and pH will multiply by binary division in about 9 hours; each bacterium divides into two new bacteria, called binary division. Provided there is a source of ammonia to trigger this, it will continue. Same for the nitrospira only some authors say this can take up to 20 hours for binary division.

The issue here is obviously having sufficient bacteria transferred to handle the ammonia from the fish. As this is unlikely for several hours, aquarists recommend very few fish in a "seeded" new tank to allow sufficient time for the bacteria to catch up. Ammonia and nitrite are highly toxic to all life, fish and plants, so it is important to ensure sufficient bacteria are present for the fish load.

However, we here come to the second related issue, plants. Live plants will immediately "cycle" a new tank. Plants use ammonium as their preferred source of nitrogen, an essential macro-nutrient. Fish and bacteria in the substrate constantly produce ammonia as a by-product, and in acidic water this changes to ammonium. The plants grab a lot of it, and use it; they are actually faster at doing this than nitrosomonas bacteria, which is why in a heavily-planted aquarium the level of nitrifying bacteria is quite low by comparison to one without plants. In basic water, the plants have the ability to internally convert the ammonia to ammonium which they then assimilate.

Provided you have sufficient plants to balance the fish load, you can add the fish all on the first day (with the plants planted) and there will be no "cycle" as such. I have set up dozens of tanks this way, as have many others. This plus the seeding from existing filter media (still a good idea) will work fine.

Byron.


----------



## CoffeeMan

So basically, if I plant live plants and rinse the old filter media in the new tank water, I should be good to go to put my new fish in right away, even if I'm using a brand new filter in the tank.


----------



## Byron

CoffeeMan said:


> So basically, if I plant live plants and rinse the old filter media in the new tank water, I should be good to go to put my new fish in right away, even if I'm using a brand new filter in the tank.


Rinsing the media in the new tank will do nothing beneficial, the bacteria colonize surfaces; putting the media in the tank, either in the new filter compartment(s) or in a nylon bag hung in the tank, is the way to do the "seeding." Then it could be removed in a couple months when sufficient bacteria would be expected to be present in the substrate, on the plant leaves, etc. Old tank water contains nothing of value, quite the opposite; ammonia and pathogens from the existing tank are something you don't need to introduce to a new tank, the fish will do this on their own;-).

But this is moot if you have sufficient plants. Bear in mind I said well-planted, sufficient to handle the ammonia from the fish. A couple plants with 100 fish in a 55g is not going to do it; but 50 2-inch fish in a heavily-planted 55g will work.

Byron.


----------

