Ammonia spike issue

Amanda Amirault

Hello. I found your template, and will provide as much information as I can. I need some help!
Are you doing a fish in cycle, fishless cycle or was your tank cycled and you had a sudden ammonia or nitrite spike?:

What is the water volume of the tank?: 55gal
What type of water are you using in your tank? (tap, well, RO/DI, other): tap
When did you start cycling the tank?: January 20
What type of filtration are you running on this tank? (sponge, HOB, canister, other): Fluval canister
If canister or HOB list all the media you are running in it. (manufactured cartridges, sponge, etc.): sponge, bio, carbon
Do you have good water agitation/surface movement?: yes - I have a fan in the tank
What is the water temperature?: 85

If fish in cycling
What is the entire stocking of this tank? (Please list all fish and inverts): 1 Flowerhorn
How often do you feed them and how much?: 2 times daily - small amounts
Are they showing signs of distress? (fish hiding, staying at the top, looking pale, torn fins, etc): staying at top, but will go down into substrate sand
Do you have live plants in the tank?: no
If so are they healthy and actively growing?: n/a

Products used while cycling
If this is a fishless cycle what ammonia source are you using? (fish food, Dr Tim’s ammonia, other): n/a
If adding liquid ammonia how often do you dose ammonia in your tank and in what quantity? (1ppm, 2ppm etc.): n/a
If using fish food as your ammonia source how much are you adding and how often?: n/a
Are you using a dechlorinater and if so, which one?: Seachem Prime
Are you using bottled bacteria and if so, which one?: Big Als (being changed to Seachem today)
Did you add seeded media from a previously cycled tank?: yes
What other products/chemicals are you using? (list them all):

Testing and cycling process
What was your knowledge of the nitrogen cycle before beginning to cycle your tank? (none, beginner, intermediate (please explain), advanced): advanced - I have 4 freshwater tanks and 2 saltwater tanks- have had them for several years without issues
What do you use to test the water? (API liquid, test strips, other): API kits
Did you test your tap water for ammonia, nitrites, nitrates and pH, if so post the results below?: yes
Have you done any water changes and if so, when?: yes - Saturday, Monday and today
How much water did you change?: 25%, 50%, 70%
Did you vacuum the substrate?: yes - Saturday and Monday
Did you clean your filter, filter media, decorations and/or glass?: yes - Saturday
If using disposable cartridges have you replaced one recently?: n/a

*Parameters - Very Important
What are your parameters? We need to know the exact numbers, not just “fine” or “safe”.
Tank water:
Nitrate: 0-5.00
pH: 7.8

Tap water:
pH: 7.0

Explain your cycling problem in detail. (Please give a clear explanation of what is going on, include details from the beginning of the problem leading up to now) I haven’t had any cycling issues and this tank has been great for a very long time. I noticed on Saturday that my flowerhorn wasn’t eating. I performed my usual maintenance on the tank: vacuum sand, clean walls, 30% water change, rinse filter media in dechlorinated water.

my flowerhorn was still refusing to eat, so I tested the water, and found the giant ammonia spike. He’s alone in his tank, no plants or decaying food. I have vacuumed the sand several times, performed several water changes, and the ammonia level refuses to drop.
Any suggestions are greatly appreciated as I love this fish and don’t want him to die.
Thank you. Amanda



That is so weird.

To start off, if the flowerhorn continues to do badly, take it out and put it in a temporary container containing fresh dechlorinated water. Yes even if unfiltered, at least for a bit of time that's better than water full of ammonia.

Second, can you do a serial dilution test by mixing half tank water and half tap water, then measuring ammonia. Then repeat with 1/4 tank water and 3/4 tap water, then 1/8 tank water and 7/8 tap water until you can measure less than 8ppm ammonia? I wonder if you just have so much ammonia that even with water changes it still registers as 8ppm.


if its not ammonia in the tap, then something went wrong with the filter.

when was the last time the canister filter was cleaned and the carbon replaced?

are you 100% sure the filter media was cleaned in dechlorinated or old tank water?

you might try taking some of the established filter media from the other tanks and placing it in this caniter.

how thick is the sand substrate?

Amanda Amirault

I cleaned the canister filter on Saturday, the same way I always do, in dechlorinated water.
The canister filter seems to be functioning as it always has.

The carbon was replaced 4 weeks ago. The substrate is 1.5-2” thick.

I went to my LFS last night and got more Prime and Frits Zyme 7 nitrifying bacteria.

The flowerhorn seems to be doing a bit better this morning, but ammonia is still reading as 8.0.

I will give the bacteria more time today and do a water change after work.

I also installed a new air stone to help with aeration of the water.
Any other thoughts on what happened here?


I performed my usual maintenance on the tank: vacuum sand, clean walls, 30% water change, rinse filter media in dechlorinated water.

It sounds like you are doing every thing right and this shouldn't have happened. How often were you doing the 30% water changes before all this started?
What other products/chemicals are you using? (list them all):
I noticed you didn't answer the question about products used in this tank. Which water conditioner are you using? I noticed you said you needed to get more Prime. Did you use something else while waiting to get more Prime? Any time I see this ammonia reading I have to wonder if ammo-lock has been added. The fact that the ammonia didn't go down even with the big water changes leads me to believe either the test isn't telling the truth or something else is causing the high reading.

Amanda Amirault

I do a 30% change once a week.
I vacuum the tank every 2 days (or more depending on his output).

I don’t use ammo-lock. As I ran out of prime after Saturday’s water change, I used the Big Als set (3 products: conditioner, bacteria and organic compound for waste)
I just did another test, to see how the bacteria I added last night was doing, and it’s still 8.0 for ammonia. (I have attached a photo)

That being said, the flowerhorn is more engaging and he ate 1 protein pellet. He has refused food for the past few days.



since you have no ammonia in your source water I would change out most of the water. I really can't imagine where all this ammonia can be coming from 'specially since you said this guy hasn't been eating. You are pulling the uneaten food out of there so I can't imagine where the source of the ammonia is coming from. I am at as much a loss as you are.

If the almost 100% water change doesn't lower the ammonia level then I have to think the ammonia test is faulty.

Amanda Amirault

I was tempted to remove all of the sand substrate to see if that helped. I had read a while back that gas pockets can develop under sand, which can surface.. one would think that they could/would contain ammonia?

that’s the last thing I can attribute to this massive spike. I just don’t have anywhere to put him while I drain out his tank. He’s fairly big lol
And he would attack my other freshwater fish if I bunked him with them for the cleaning process…


I was tempted to remove all of the sand substrate to see if that helped. I had read a while back that gas pockets can develop under sand, which can surface.. one would think that they could/would contain ammonia?
No, the gas pockets that develop is build up from anaerobic activity in the sand bed. Not ammonia as that's the wrong part of the nitrogen cycle.

This is a very weird situation. Are you certain that you didn't forget to dechlorinate your water at some point?

Even if you rinsed all your media in tap water this wouldn't happen. You would have to soak your bacteria in chlorinated tap water for almost an hour to cause a massive bio die off before something like this would occur.

Or....the test is bad....but the fish is behaving as if he's stressed so im inclined to believe the test is telling the truth.


Since doing close to a 100% water change isn't really doable with a fish this size the second best option is several 50% water changes. The main reason for changing so much water is to get the ammonia out of there. If the water changes aren't lowering the ammonia then something else is happening. If this was happening in one of my tanks I would do no less than 2 50% water changes a day until all the ammonia was gone.

I can't imagine the sand substrate causing it but go ahead and stir the sand while doing the water changes. If by any chance the ammonia is being produce somehow by the sand stirring it should release and pull more of it out.

Amanda Amirault

I will try doing multiple changes today.
my flowerhorn is eating again, but I’m only providing small amounts to control the bio load.
I did a control test on my Cory tank to see if my ammonia test is bad. It came back at 0.00 while the flower horn tank came back at 8.0.
I will try stirring the substrate and pull out 50%.
then do another 50% later today.
I am hoping that over the weekend I can get this sorted out!
Thank you for all of your help! If I find anything else, I’ll let you know!


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