Weird nitrite problem

[NibyNool]

Hi everyone,

I'm usually found haunting the chatroom when most others are asleep, but I have an issue that has warranted me creating this thread rather than just asking fellow chatters.

Tank Description:
I have a 20 gallon tank. It's well on it's way to being heavily planted, it has more plants than an average planted tank, but isn't at the point were i'd add it to the 'heavily planted' section just yet. The tank has a 3-4mm gravel substrate with some 1-2mm substrate near the back where the majority of the plants are. The substrate is about an inch deep. Filtration on the tank is an external canister filter rated at 300gph. I have a pile of driftwood in each corner. Heating is taken care of by a 300W Hydor ETH inline heater on the filter return. The tank has DIY CO2 (which is running VERY slowly due to the current cold temperatures in Australia). I added some Osmocote ferts under the substrate. The aquarium has been cycled for around 5 weeks.

Current Stocking:
This aquarium currently has 21 Neon Tetras. For plants there is some Java Moss, Water Wisteria, Ambulia and Anubias.

The Problem:
My issue is that when I do a nitrite test at night the reading comes back extremely high, but in the morning it is always 0. I have done the test with both an API and a Hagen test kit. These fluctuations have only started occurring in the last week, approximately 1 week after adding the Osmocote, and around the time I added 10 Neon Tetras and the Java Moss.

Does anyone know what could be causing my nitrites to increase during the day?

 

[dbosman]

One consideration is that there is nitrate from the normal bacterial cycle in every tank and nitrate from your fertilizer. They aren't necessarily the same chemically, but they would register on the inexpensive test kits we typically use. If your ammonia and Nitrite are stable, I'd not worry too much about consistent daily nitrate fluctuations.

Two things come to mind to explain your fluctuations.
A) Some of the Osmocote got exposed to the surface and is breaking down more rapidly then it would other wise, or your fish may be exposing some during the day.

B) During the day your fish are active, eating, digesting and pooping. At night when the fish are resting or sleeping the bacterial filter seems to catch up.

 

[NibyNool]

Thanks for the response. It's along the lines of what I was thinking.

A) Some of the Osmocote got exposed to the surface and is breaking down more rapidly then it would other wise, or your fish may be exposing some during the day.

I doubt this is the issue as neons tend not to stir up the surface and I can't see any of the osmocote on the surface.

B) During the day your fish are active, eating, digesting and pooping. At night when the fish are resting or sleeping the bacterial filter seems to catch up.

This is a definate possibility, but I don't think the bioload from 21 neons is going to create the issue.

It is possible that the combination of the Osmocote and the bioload is creating the issue, but it does seem like a large fluctuation on a daily basis. If this is the case, do I base my readings on the morning test or the evening test?

 

[jpappy789]

Nib, are you showing any nitrate?

 

[NibyNool]

Nib, are you showing any nitrate?

Nitrates are 0, but have been since the tank was planted.