muddyfox wrote:

Hi Everyone,

I usually run a full fishless cycle with a new set up but this time I
am setting up a 40 litre nano tank (low tech planted) and it happens to
be time to change one of the sponges from my mature 90 litre planted
tank filter so I've taken the old sponge and cut it to fit the little
filter in the new tank.

I've started to run a fishless cycle by adding ammonia as usual and my
parameters unsurprisingly indicate that the tank is cycling almost all
of it right away.

20hrs after dosing 1 drop per gallon NH3/NH4+ parameters a

NH3/NH4+ = 0.25ppm.
NO2 = 0.25ppm but still registering
NO3 = 20ppm.

Normally I wait for a Nitrite spike before reducing the Ammonia dose to
1/2 drop per gallon and then count the tank as fully cycled when it can
clear this dose in 24 hours. Previously I've been able to fully stock
a tank in this condition and have never seen ammonia or nitrite after
adding the fish. Since this tank (using old media) is clearing almost
all the high dose right away I'm thinking of testing with the lower
dose and if all paramters are clear 24hours later then prepare for the
fish. It seems reasonable to me but I wondered if someone with
experience using old filter media might be willing to check me as I
don't want to risk the fish without a second opinion.

Well, when using old media I put quite a bit and just put the fish (not too
high load) in and go and find the tank is cycled almost immediately. It
might do a tiny minicycle, but generally everything is fine. It may take a
week to settle completely.

The bacteria should populate quickly with a good start from old media.