Help! Mature tank cycling?! (fish in tank)

[KimiS]

I have a 240l tank that has been running for over 6 months with no problems. A few weeks ago I added some new stones as decoration and after a couple of days my ammonia levels suddenly shot up. This seems to have triggered a "mini cycle" - is this possible?!

Of course I threw the stones out (I tested them separately and yes, they were the cause of the ammonia - and yes, I realise now I should have done that before adding them to the aquarium!)
But since I threw them out my readings for Ammonia, Nitrate and Nitrite have been weird - and very high. I managed to get the Ammonia down by frequent water changes and squeezes from sponges in my other healthy tank. Yesterday my Nitrite spiked at 1.0.

I did a 50% water change and this morning readings this morning using API test kit were:
Ammonia 0ppm
Nitrate 10ppm
Nitrite 0.5ppm

My question now is: Having done a 50% water change this morning, what do I do next? Should I add Amquel+ to neutralise the remaining Nitrite? Or or Tetra Safe Start to add more bacteria? Or both? Which is better Tetra Safe Start or StressZyme?

I should mention that the fish in the tank are 2 x 5" Clown Loaches, 3 Black Skirt Tetra and 5 Bosemani Rainbowfish. All seem outwardly OK but I am not sure. The rainbows are often at the surface so I have increased aeration.

Any advice would be appreciated![/list][/list]

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[Diana]

Keep up the water changes and use Amquel or Amquel Plus, or Prime... one of the dechlorinators that will lock up ammonia. Since the ammonia is down, just the regular dose is fine. Prime will also help with nitrite, and I think Amquel Plus will, too. Follow label directions.

While nitrite shows add 1 teaspoon of salt per 20 gallons (5 ml per 80 liters) to help prevent Brown Blood Disease.

Tetra Safe Start is the Nitrospiros and other bacteria that are the actual nitrogen cycle bacteria. If your nitrifying bacteria have had a die off, then add some of this product. From those test results, it looks like the bacteria are recovering.

Stress Zyme is not. I would not waste my money on it.

How did the stones contribute to the ammonia?
Yes, anything that adds ammonia or kills the nitrifying bacteria will trigger an mini cycle. Looks like that happened here, and with your quick action in doing water changes, and identifying the source of the problem the mini cycle is indeed a small one.

[KimiS]

Hi Diana,

Many thanks for your reply. It was much appreciated! It was indeed a "mini cycle", and I didn't realise this could even happen in a mature tank. I guess I was getting a bit panicky.

I did another water change and used Tetra Safe start which seems to have worked and the tank now appears stable again. Fingers crossed! Ammonia, Nitrate and Nitrite have all been reading 0ppm for the past 48 hours. The Clown loaches seem fine, but one of the rainbows seems to have ammonia burn? Red open sore spots on both sides near gills. So I am dosing the tank with Melafix.

Apart from that I seem to have got away lightly. As for the stones/rocks that caused it all - they seem to have had a metal content that caused the ammonia. They were grey/white with a reddish stripe. I am still not sure what this was, and my LFS where I bought them did not want to know. So I won't be going there again!

Thanks again for your help. I have seen lots of threads on here with your tips and advice - always so very helpful.

[Diana]

I am not sure how a rock could cause an ammonia spike, but perhaps some of the metals in the rock were bad for the nitrifying bacteria, and when some of them died off the remaining bacteria were not enough to handle the fish waste.

If this is the case, then using a product that locks up heavy metals (contains chelators) would be a good move. Then, with each water change do a thorough gravel vac and these metals will gradually be eliminated.