Tank Has Uncycled?

[Linway]

Hey all,
A few weeks back I posted about how to change filter as my previous one had gotten extremely loud to the point it could be heard in other rooms. Anyway I bought a new filter (Fluval U2) and did as instructed with changing. I took the media from the old filter and packed every bit of it that I could get into the new one.
 
Anyway, I just did a water test now and it appears that my tank has uncycled.
Previous test values at the time of the test:
pH: 7.4
Ammonia: 0.25ppm (It's normally 0 but I'm just going off of the last test I had written down)
Nitrite: 0ppm
Nitrate: 20-40ppm
 
New test values as of right now:
pH: 7.4
Ammonia: 0.25ppm
Nitrite: 0ppm
Nitrate: 2-3ppm (API test kit, darker than the 0ppm yellow, lighter than the 5ppm orange)
 
What do I do? This isn't a new tank, it's been cycled for a good 4+ months now and I've never seen any spikes in ammonia or drops in nitrate until right now.
Is this a problem with the filter? Would the bacteria have grown on the old filter casing rather than the media?
 
I should add the new filter has been in for almost 3 weeks now and the fish are showing no signs of stress. I have to assume that something is keeping the ammonia down if after 3 weeks it isn't high regardless of low nitrate levels.
 
Cheers guys
 
p.s. I just phone the LFS that usually gives me good advice and told him the test readings. He replied "that's fine, you want all 3 as low as possible", is this right? For a long time I've been under the impression you want nitrate highish but not so high to cause a problem (so keeping it below like 80ppm with water changes). is the LFS wrong or is my assumption wrong?

 

[Lillefishy]

Nitrite & ammonia need to be zero, nitrates you want to try & keep them under 40, lower is better

 

[daizeUK]

I would not be overly concerned about an ammonia reading of 0.25ppm, particularly if that's after 3 weeks in a fully stocked tank. At this stage I would say keep an eye on your water quality but otherwise you don't need to take any action. Keep watching your fish for signs of stress.

Proceed with a usual weekly water change of about 50% and don't worry unless you see ammonia rise to 0.5ppm or if nitrite starts to show.

As for the falling nitrate, that's not usually possible unless you have plants or special media absorbing the nitrate.

The LFS is correct in that lower readings are better. If you have plants then you should aim for a nitrate reading of about 20-30ppm in order to feed the plants otherwise there is no reason to have high nitrate. The fish will benefit from lower nitrate but in reality anything up to 40ppm nitrate is not a problem for most species of fish.

It is correct that ammonia and nitrite should read 0ppm in a cycled tank, but it is also true that home test kits are often not sufficiently accurate to warrant concern with a reading of 0.25ppm. With the heavy seeding you gave your new filter I'd expect you should be just fine.

 

[Linway]

I would not be overly concerned about an ammonia reading of 0.25ppm, particularly if that's after 3 weeks in a fully stocked tank. At this stage I would say keep an eye on your water quality but otherwise you don't need to take any action. Keep watching your fish for signs of stress.

Proceed with a usual weekly water change of about 50% and don't worry unless you see ammonia rise to 0.5ppm or if nitrite starts to show.

As for the falling nitrate, that's not usually possible unless you have plants or special media absorbing the nitrate.

The LFS is correct in that lower readings are better. If you have plants then you should aim for a nitrate reading of about 20-30ppm in order to feed the plants otherwise there is no reason to have high nitrate. The fish will benefit from lower nitrate but in reality anything up to 40ppm nitrate is not a problem for most species of fish.

It is correct that ammonia and nitrite should read 0ppm in a cycled tank, but it is also true that home test kits are often not sufficiently accurate to warrant concern with a reading of 0.25ppm. With the heavy seeding you gave your new filter I'd expect you should be just fine.

 
Oh ok, yeah I wasn't worried about the 0.25 ammonia, it was the low nitrate that concerned me really. Thanks for clearing that up

 

[EllieJellyEllie]

Also, if you use Prime it tends to give false ammonia readings. My tank is normaly between 0 and .25 when I use prime, and when I dont its 0.