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Tank cycling: small ammonia spike, then... nothing?

792 Views 4 Replies 4 Participants Last post by  Diana
I started cycling a tank at the beginning of the week (my first tank in years and first ever planted), and seem to have hit a bit of confusion with my ammonia readings. I added in some juvenile mosquitofish from the backyard pond as an ammonia source, and was getting very low readings for a few days, peaking at somewhere around .30 ppm, with zero nitrates and nitrites.

Yesterday, though, the measured ammonia levels dropped to zero, and read as zero today as well. Nitrite levels tested zero both days... and nitrates as well.

Plant-wise, the tank currently has a six small java ferns, a tiny windelov, one Hygrophila corymbosa 'siamensis,' and a few stems each of rotala rotundifolia arcuata and ludwigia repens. Is it possible the plants have been processing the ammonia as a nitrogen source rather than the bacteria colonies establishing themselves, hence why there was no noticeable nitrite spike and only a very small ammonia spike? Would it be safe for me to relocate the cycling fish and add in the tank's first set of permanent residents, a small school of otocinclus? I'm kind of at a loss here.
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The plants are probably eating it. With no nitrates though, it's hard to say if it's really cycled or not cycled at all since the plants are eating it.
What size tank? What test kit are you using?

It's possible the plants are processing it, yes. I doubt the tank is cycled after two days but the plants are probably helping in the meantime. Otos can be sensitive fish, not sure if trying to cycle with them is a good idea. I'd be a bit wary of putting something from outdoors into the tank though; who knows what else you're adding in there, but maybe that's just me lol

A few days isn't really long enough to gauge much. Tank size would play a role as well; if it's a large tank with a few small fish the toxins will rise more slowly due to the water volume. I'd say to wait it out a bit longer.
20L and the fish are still pretty small; guess I'll wait it out for a while rather than risk it.
Remove the fish and add real ammonia. Be very careful with the dosing and monitor it for 24-48 hours. Check ammonia, nitrite and nitrate.
I would test this with different levels of ammonia.
1 ppm
2 ppm
3 ppm

If the ammonia you add and nitrite both read 0 ppm after 24 hours the tank is cycled for the amount of ammonia you have added. It does not matter if it is the plants or the bacteria or both. They are all viable bio-filters.
Go ahead and stock the tank, but do not exceed the level of ammonia that the tank can handle:
1 ppm: perhaps 1/4 of normal stocking, or else continue with the fishless cycle.
2 ppm: perhaps 1/2 of normal stocking
3 ppm: Go for full stocking.

If the tank does not do well in these tests, then do the fishless cycle. Then you will know the tank is ready for whatever livestock you want to add.
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