Keeping a fishless tank cycled

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Fish Fanatic
Oct 11, 2023
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I have a tank with brand new filter media that has cycled in 4 to 5 days using

When I say cycled, I mean it has reduced 2ppm Ammonia to 0ppm Ammonia and 0ppm Nitrite within 24 hours. In fact, it has done this twice now, to rule out ammonia evaporation. I only took it to 2ppm Ammonia as the initial fish stocking will be light.

My question being, I will not be adding the fish just yet. To keep the filter media cycled, how much ammonia should I dose in a 24-hour or 48-hour period? Obviously the answer relates to ppm levels. I believe a constant reading of ammonia is not required, is that correct?

I use Dr Tim's ammonia btw.
From the fishless cycling method on here -

If for any reason you are unable to stock the tank when it is cycled, you can continue adding ammonia to keep the tank cycled.

The bacteria do not need to be fed every day so you only need to add ammonia every 2 or 3 days. If the wait time to add fish will not be more than a week, you can just add the snack dose amount 2 or 3 times in total and things will be fine. However, if the wait time to begin stocking will likely be longer than one week, do not use the 1/3 snack dose, instead, use the full ammonia dose you did when cycling. You can do this for many weeks if needed.

Keeping a tank without fish fully cycled for extended amounts of time requires doing weekly 50% water changes. Do these on the days you plan to add ammonia and do the change before adding the ammonia. If you do not do weekly water changes, nitrate will build up and KH levels will drop which can cause unwanted issues with the cycle. Further, other things the bacteria need may get used up and normally these get replaced by the new water going in. Of course, remember to do as big a water change as possible before adding fish, even 80%+ is fine.

The 'snack dose' is enough for a reading of 1 ppm and the 'full dose' is 3 ppm.
From the fishless cycling method on here -

The 'snack dose' is enough for a reading of 1 ppm and the 'full dose' is 3 ppm.
This link is really helpful @Essjay and @TwoTankAmin - I would not have considered changing any water during an actual cycle. It makes sense that there may be elements other than nitrate reduction that could help keep the tank well cycled in the absence of fish. Thank you both.
Shops tend to get a lot of fish in at once, especially wholesalers. It can take a week or two to move fish about so they’ve got enough empty tanks for when the order comes. The tanks can go a week or two empty and with no ammonia added, and when they’re suddenly heavily stocked again the bacteria all kick in.
To be on the safe side, since every tank / filter is different, adding ammonia every few days as the guide says is a wise route. The bacterial colony will adjust its size according to how much you’re adding. For most tanks 1ppm is more than you’ll need, but you can add more and it makes no difference. The colony size will adjust, and then adjust down when you add fish.

High nitrates won’t stall a cycle but I believe they slow it down. You can change as much water as you want during a cycle, (remember to re-dose ammonia or whatever), so it doesn’t really make sense not to. It replaces KH and trace minerals used by the bacteria.

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