What caused nitrite spike

[laka]

I just lost half my fish. Last night before bed I was admiring them at how much they have grown and their beautiful colours and this morning I am mopping up the dead ones. Fish still alive appear to be breathing heavily.

Doing a big water change and added an air stone in tank. I have a heavily planted non CO2 tank. My feeding and plant dosage regime has been the same the last 12 months. I only do a 30 % water change once a month.
I have SENEYE monitoring system. pH 6.96, ammonia 0.001 ppm. Nitrates about 10ppm using test kit but nitrites are 0.5ppm.

Last night before I went to bed I dosed the tank with the weekly Seachem Iron, Flourish and Excel at normal dose. I used a new bottle of Excel. I have a canister filter that is cleaned every 3 months but sponge cleaned monthly.

So I would dearly love to know what caused my nitrites to spike?
Also why did nitrites spike in the absence of an ammonia spike? How can this be explained?
Bewildered and numb from the loss.

LAKA

 

[tanker]

2 different things. Nitrites of 0.5ppm did not kill your fishes, this is from the dead fishes.
Something else killed them.

 

[laka]

2 different things. Nitrites of 0.5ppm did not kill your fishes, this is from the dead fishes.
Something else killed them.

Hmm. I cleaned out my canister filter. Besides dark murky water at base no foul smell that may indicate bacteria die off.

In fact tank water has nice sweet smell to it.
I did two 70% back to back water changes and still have nitrite reading of 0.5 to 1ppm. PS. Texts say nitrite lethal dose commences at 10mg/l. How many ppm is that?

So assuming nitrite by product of fish fdie off, what caused so many to die overnight?
As said before the only additions last night were plant fertilisers, 2 squares bloodworm being their weekly treat and 2 algae wafers.
Laka

 

[tanker]

Aside from dosing did you do anything else? WC? Filter stopped?

 

[laka]

No. Nothing. No water change filter Working well.
I did notice considerable mulm- dead plant matter accumulating in one area of the tank. I do a water change and gravel vacuum once a month. Could this decaying plant matter be the culprit? My tank is super heavily planted, no free gravel to speak off. 400litre tank.
I am thinking of doing fortnightly 20% water changes with gravel clean and check nitrites weekly. Basically Improve fish husbandry.

PS. I note doing a Google search it is not uncommon for established tanks like mine to undergo a nitrite spike for no apparent reason that we are aware of, such as fish death, blocked filter, over feeding.
Maybe there are some other variables that we are not familiar with that affect nitrites.
laka

 

[Rbishop]

What size tank and details on exact fish loading, please. Full tank shot?

 

[laka]

400litre tank, 3 angelfish, 10 rainbowfish, 3 bristlenose, 1 red tail shark and lots of plants.

Laka

 

[tanker]

400litre tank, 3 angelfish, 10 rainbowfish, 3 bristlenose, 1 red tail shark and lots of plants.

Was this the initial stock before the deaths? And what died?

 

[laka]

Initial stock in tank set up a year ago. Lost the large fish. Small ones survived. Lost 1 Angel, 5, rainbows. I have a thick 10cm soil substrate,- laterite, and gravel on top. I suspect the nitrite spike was a result not cause of fish death as it was not very high like Tanker said. Today nitrites zero again.

I suspect my tank experienced a pulse of noxious gases escaping from substrate that sucked O2 temporarily causing suffocation. Rotten eggs gas? Hopefully gravel cleaning fortnightly will avoid repetition. That is the only explanation I can think of.

laka

 

[laka]

Ok after much after thought over the weekend I think I may have solved the fish death mystery.
The fish most likely died from an overdose of seachem excel. I remember accidentally spilling more in but did not think much of it The ensuing deaths caused the nitrite spike.this hypothesis carries more weight than rotten egg gas since I never experienced foul odour from tank.
Laka