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Large Ammonia spike...help

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Hi all

after cycling my tank for 2-3 weeks with very large amounts of seeded media and having the ammonia settle down to 0ppm for a few days and nitrate was steady at 5ppm I thought all was good and everything was stable.

Then when I checked the levels this morning I found a HUGE spike straight to 4ppm ammonia(Ive never seen such levels b4) nitrates were still 5ppm ph steady at 8.0

I did a quick 25% water change to lower the ammonia with no change.

So should I keep changing water daily to bring it down as the ammonia is very high?.....was my last water change to raise the ph effect something?....

they only get one feed a day which they consume in 10 seconds?

any ideas?



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Throw some prime in it will bind your ammonia up for 24 hours

was your ammonia stable when the tank was empty? If so the bacteria probably aint well enough established for the livestock in your tank

how big is your tank and how many fish are in it

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ok tank 600liters and sump 200litres, had been cycling for 3 weeks. before the crash I had stablized the ammonia down to 0ppm for a few days with nitrates at 5ppm nitrites 0ppm and ph 8.

14 african cichilds and 4 baby bristlenoses

So after 2 30% water changes morning and night, which made the ammonia levels half each time. We were left with .5ppm ammonia, went to bed and woke up with 0ppm ammonia this morning....yeah......what a rollercoaster.

How it could be 0ppm ammonia after the cycle finished and then plunge to 4.0 ppm over night and then 2 big water changes which returned the levels back to 0ppm ammonia and a large nitrate jump to 20ppm from 5 ppm from yesterday...?????? very strange, but all is good now.

thanks for everyones input ;-)


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Full filter cycles take longer than a few wks. At a few wks it would of been ready for 1/4-1/2 that stock level, then add more gradually as the filter bac matures. With the seeded media things can happen quickly though. What were you feeding the filter before adding fish? Dirty fish tank water from other tanks? Liquid ammonia? Crushed fish food? Rotting prawn or fish?

Gotta feed the bacteria up to your stock level that's getting put in all at once or add fish gradually, a few at a time, to immature systems.

It was the (hopefully) last spike of your cycle from the sounds of things but the actual bacteria colonies will take a fair bit longer to mature & become 100% effective. Cycle was nearly completed but perhaps not ready for an instant stocking of 20 odd fish. That's why nitrates went up so much overnight, lots of extra food for bacteria to multiply & consume.

Should be almost finished cycling now, just watch for spikes & don't feed too heavily. At least with your nitrates coming up you know the nitrite consuming bacteria are established as well as the ammonia consumers.

As for the 2 water changes taking ammonia levels from 4.0 to 0, I think your dechlorinator may have helped with that. If you're using Prime or Supachlor they will bind up harmful ammonia for 24-48hrs so it can be dealt with at a steady rate.

Best of luck mate, hope all goes well with no more rollercoaster chemical spikes :)

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I think you may be confused as to what the cycle actually is.

Is essence it is establishing enough ammonia/nitrite eating microbes to consume the current amount of ammonia/nitrite being produced.

so........... when you added all the new fish........... there was then more ammonia and nitrite being produced than there was previously.

This means that until the ammonia/nitrite eating microbes bred up into sufficient numbers to be able to consume the ammonia/nitrite now being produced.......... there was going to be more left over.

It takes about a week for microbes to build up enough to handle the addition of a few more fish to an established aquarium.

to compensate for this, after adding new fish, we only very gradually increase the amount of food we are adding to the aquarium.

We also test ammonia/nitrite at the end of this week, and if there is any detectable, we wait longer before adding more fish.

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thanks Pete and Donny for your kind words

I have not been too good explaining the situation.

I have added 2 fish tanks together.

One tank had been operational for 6-8 months with lots media in the sump and carrying 10 or so fish.

the second tank is new from 3 weeks ago with some seeded media and started with 4 fish.

I am having my house painted and needed to move the established tank inhabitants to a safe spot away from the paint fumes and thought all the well established media could also help the new tank.

So they all went in together and after a couple of weeks the media I think seems to have finally caught up.

I think I will leave them all together now as they are happy and its a very nice tank.

I hope this makes sense now. Im a little lazy normally with explaining things....sorry for the confusion

thanks again


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Ah........... that makes more sense.

Basically when you moved the tanks around you damaged lots of biofilms covering the surfaces of gravel/ornaments etc.

This has died which has resulted in ammonia.......... but the filtration microbes have rapidly bred up and converted them to nitrates.

Hence the sudden surge in ammonia, and then drastic increase in nitrates.

1) you saved the day with water changes

2) everything was ok in the end


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