Ammonia Question

[Benunited]

Hi folks

Quick question about ammonia.

I recently (I think) completed the fishless cycle for my 2nd tank - getting 0 ammonia, 0 nitrite and trace nitrate levels continuously before adding fish a couple of days ago.

This tank is a 30 litre biorb which I'm using as a quarantine tank before adding fish to my other tank, which is fully fishless cycled and has been running well for a good few months now.

From past experience I know the tank can safely handle 8 small fish - it used to hold 4 guppies and 4 cardinal tetras and never had any ammonia or nitrite once it was cycled.

Now I've restarted the tank, completed the cycle and added 8 tetras.

Trouble is my tests are now showing low levels of ammonia. What's puzzling me further is the nitrite reading is zero (good!) with low nitrate levels.

So, if the tank is fully cycled, what's happening.

Can I have some ammonia, no nitrite yet some nitrate? Well, obviously I can... but why has this happened and what can/should I do?

All advice much appreciated.

Thanks!

Ben

 

[Corleone]

How did you cycle it? (what was your ammonia source, how long did it take, any details at all)

Even after a fishless cycle, it is possible to overwhelm the bacteria you built up and get an additional minicycle if you add a heavy stock of fish right away. Cycled isn't a yes/no question, it's about amounts. You may have just added a higher load than the fishless cycle prepared the tank for (eight cardinal tetras, which I assume are the ones you got, in 30 liters is a big immediate stock).

If that's the case, you can treat it like a fish-in cycle and the filter will catch up.

 

[JoshuaA]

Also how long was it since you had last fed the bacteria in your Biorb tank? if its too long you may have actually lost the bacteria. Unless you fed up to the point in which you introduced the fish.

How severe is the Ammonia reading? I hear a lot of people do detect minuscule traces of Ammonia in their tank even once cycled. Although if it's showing up a good 0.25 Ammonia you may have some concerns, if you were good and fed the bacteria I think doing a few water changes will suffice until your filter keeps up.

Just finished a Fish-less cycle with my girlfriends tank in a 60L and we only added 3 small juvenile fish to begin with. Like Corleone says you may well of over done it with the 8 being introduced and shocking the filter.

 

[Gvilleguy]

And did you test the base source water for ammonia? My tap water tests out 0.25 ammonia on its own, which kind of sucks. I'll actually be adding ammonia when I have to do water changes. I only asked in case you did a large water change before adding your fish, and if you were adding ammonia without realizing it.

 

[Benunited]

Thanks folks!

Used pure ammonia right up to the day before I added the fish. Also had some bogwood in there from my other, fully cycled tank, which sped the processs up nicely.

Seems to be fine now - no ammonia for the past 24 hours, testing at 8 hour intervals. Also made a water change.

Was maybe just the cycle catching up.

What I had been wondering, though, if a cycle is complete or incomplete..

If ammonia turns into nitrite, which in turn turns into nitrate...

How do you have some ammonia, no nitrite but some nitrate? Bit puzzled!

 

[Benunited]

Meant to say, found that the ph had dropped to around 5.5/6 which I guess could have stalled the cycle...

Though the ammonia returned to zero before I could treat the ph drop... so if the ph was a factor the tank continued to cycle properly even with this low ph reading

 

[Corleone]

What's the normal pH? pH can crash during a fishless cycle (or for that matter during normal operation if you go too long between water changes), particularly if your water has a low kH. Did you do a big (~90%) water change right after the cycle before adding fish? That'll "reset" your water stats and prevent that from happening afterwards.

I had a couple pH crashes doing my first fishless cycle, and in my experience the cycle seemed to stop dead, but if I did a big water change right away it would pick right back up where it left off, as if the bacteria were still alive, but unable to eat.

 

[OldMan47]

Do not mistake a fully cycled filter that is now running with fish as being the same as a fully cycled filter being checked before adding fish. A newly established filter being checked for ammonia and nitrite must demonstrate its ability to handle a huge fish load, one represented by your 5 ppm ammonia addition. A fully functional filter in a populated tank is capable of moving every bit of ammonia those fish produce but may not be able to move a 5 ppm dose of ammonia. Your previously cycled filter has adapted to whatever fish stocking level you have. It may take it a few days to reach a condition where it can fully process 5 ppm of ammonia like a newly established filter would. Almost none of us even try to stock as many fish as are equivalent to that 5 ppm in a new cycled filter. Instead we may be stocking at levels that might compare to 2 or 3 ppm of ammonia. The filter will take a day or two to recover to the bioload of that bigger stocking if you go back to measuring the filter in fishless fashion.