Strange Cycle Problems In Established Filter (New Tank)

[jnms]

Hi all,
 
I have a bit of a problem with an ammonia spike that I just can't get seem to end.
 
I used to have a 200L tank, stocked with 3 Angels, 6 Mollys and a Bristlenose.  The tank was filtered with a Fluval 305.
 
About 2 weeks ago I changed the tank for a 100L and restocked it with new fish; 12 Neons, 4 Honey Gourami and my old Bristlenose.  I realise this is slightly on the heavy side for stocking, but the bio load should be comparable to what I had previously.  Whilst the tank is new, I moved the Fluval 305 over - there was only a few hours downtime for the filter.
 
However the problem started about 2 to 3 days after I set the tank up, I started getting ammonia spikes of 0.5ppm.  Now over 10 days later, I continue to get the same 0.5ppm of ammonia.
 
I'm not sure what caused the spike (new tank, new stock, loss of bacteria from gravel).  I kept some of the gravel from the previous tank, but only a small portion of it.  The current tank has new decor, I didn't transfer the previous decor.
 
This is what I have tried so far:
Cleaning the filter pipes to ensure nothing is stuck in them.
Checked the filter to ensure there is nothing rotting in there.
Checked the tank for anything dead or rotten.
 
Water Change 50% per day (2 lots of 25% one morning the other in the evening)
 
 
I assumed at first that I was in a mini-cycle due to the tank change over.  But after 10 days I would have thought the mini-cycle would have ended.  I am at a loss of what to try next.  These are my current water readings:
 
Ammonia:  0.25ppm (after 25% water change)
Nitrite:  0ppm
Nitrate:  40ppm
 
Any and all help most welcome!  I am so concerned that I am going to lose the fish...
 
Nitrites never increase past 0ppm, so maybe the cycle has crashed - or maybe the nitrites are being converted to Nitrates, is there anyway to tell?
 
 

 

[snazy]

You probably just happened to have a lot of the bacteria in the old substrate in the 200L tank, so carrying over just the filter didn't transfer all bacteria.  How long the "mini" cycle will last is hard to tell.  It still should last shorter than a normal cycle considering you are using the cycled filter. I don't think switching off the filter for a few hours would kill that much.
As for the lack of nitrIte spike, it's possible you carried over more nitrIte bacs, than ammonia bacs for example. On another hand there's no easy way to tell whether the nitrItes are being converted to be honest, or whether in fact much ammonia is being converted. What's the nitrAte tap water level? If it's the same as in the tank, then there isn't much conversion. But either way the nitrAte test is so horrible, you can't rely on it.
As long as you are persistent with the daily large water changes and keep the ammonia at least below 0.25ppm, then the fish should be ok. Just don't give up.

 

[jnms]

Thanks for the reply snazy.
 
I was a bit worried that 10days is too long for a mini-cycle.  But I guess even if the cycle has crashed, it will eventually pick up again.
 
I am continuing to do the water changes.  Today I ordered some Seachem Prime, which should be here within a day or two - should hopefully help the fish somewhat until the filter completes its cycle.

 

[snazy]

You should be fine. Change as much as water as required daily and dose Prime and the fish should be fine. That filter should pick up early or later.

 

[liamhuckle]

Hope you sort it im going through sonwthing similar but upsizing not downsizing like you say snazy could be down to substrate never even thort about itas the enphasis is always on filter and media