Unexplained death in QT due to mini-cycle?

Hello all,

I've got a 10gal QT tank, fully cycled prior to adding fish (0 ammonia, 0 nitrite, 5 nitrate). I added 6 cherry barbs to it last weekend, and they've mostly been doing fine, swimming and happy. I feed them either flake food or broken up algae wafer, only enough that will be eaten in 5 or so minutes, every other day. I check the water chemistry every other day and on Wednesday, I noticed the ammonia went up (0.25 ammonia, 0 nitrite, 2.5 nitrate). I dosed with a small amount of Seachem Prime and kept a close eye on the tank.

Yesterday, one of the fish had a red spot on its nose, almost like an injury just beneath the skin. I checked the chemistry (0.25 ammonia, 0 nitrite, 2.5 nitrate) and dosed Seachem Prime again. This morning that same fish was on it's last legs - it was pale, and listless, lying on a fake plant. When I moved near the tank it frantically shot about swimming at the surface, and then tumbled down into the tank and was struggling to move at all. I didn't imagine that it'd recover and so euthanized it. My concern is that the ammonia (0.25ppm) was too high and might start to harm the rest of the fish too.

Was this just a weak fish that was already on it's way out? Did the ammonia do this to the fish? Has anyone encountered this before, a cycled tank almost un-cycling after fish have been added?

 

0.25ppm should not be enough to kill the fish, no. I also doubt your tank uncycled either - by now ammonia would probably rise higher than 0.25ppm if that was the case. It is common to register 0.25ppm in cycled tanks, especially once it is stocked.

Most likely it is a weak fish.

 

Thanks for getting back to me. I guess I'm just very nervous because I've only been in the hobby for about 7 months, and take each death personally.

I'll keep my daily monitoring of the water chemistry and otherwise watch them quite closely.

Just for my own informational purposes, what would ammonia poisoning look like in fish? I guess shooting to the surface and general weakness made my mind immediately go to an issue with the chemistry.

 

Sorry for your loss. When did you do the last water change on that tank, and how much did you change? Could you do a big one right now?
Could it be that other water quality issues may be the cause? Minerals, temperature, pH come to mind.

 

Water change is your friend. Aged water

 

Sorry for your loss. When did you do the last water change on that tank, and how much did you change? Could you do a big one right now?
Could it be that other water quality issues may be the cause? Minerals, temperature, pH come to mind.

Prior to housing the 6 cherry barbs in the QT, once I was sure that it was fully cycled, I did a roughly 90% water change on the tank - this was about two weeks ago. I tried to not disturb the gravel too much either.

There's a small cave that none of the fish seem to care for, so I'm thinking about adding several of the fake plants back into the tank. There's currently one or two, but maybe an underwater jungle may ease their stress?

 

Did you mix nitrite with nitrate? Most test kits can't measure 2.5 nitrate

 

Did you mix nitrite with nitrate? Most test kits can't measure 2.5 nitrate

That's a good catch. I didn't, but the colour that the Nitrate should've turned according to my kit (kind of a rusty orange) wasn't fully rusty orange after ten minutes. So (not being chemically-minded) I decided to split to difference and say that it wasn't fully where it needed to be (at 5.0ppm).

 

That's a good catch. I didn't, but the colour that the Nitrate should've turned according to my kit (kind of a rusty orange) wasn't fully rusty orange after ten minutes. So (not being chemically-minded) I decided to split to difference and say that it wasn't fully where it needed to be (at 5.0ppm).

Ah okay I wouldnt worry too much about nitrate then. I would be worried bout ammonia readings though, any reading even if low is a bad sign.

Red gills, heavy breathing is a sign of ammonia toxicity. Might need to do more water changes or feed less