Cardinal tetras dying

Everything is going haywire this week.

Yesterday, my betta got aggressive and attacked at least one of my cardinal tetras, taking a chunk out of his tail fin, he didn't make it.

Later that day, after separating the beta, another cardinal began drifting around the tank and struggled to stay upright. I removed the affected fish from the tank. He simply couldn't stay upright and died a few hours later. I chalked it up to a fatal injury from the beta.

This morning, I found another cardinal, separated from the school gasping for air at the surface and drifting around staying vertical. I put him in a container and he's exhibiting the exact same symptoms as the previous cardinal:

- lying on his side
- unable to move
- no visible injuries

I tested my water and the ammonia is at 0.2, so not great, but still. Is it enough to get 2 cardinals sick?
I've been doing water changes every 2-3 days for about 2 weeks and my ammonia has been around 0.1 - 0.2. If it's bad enough to make them sick, why is it only happening now?

Did yesterdays beta incident stress them out?

 

If there is ammonia present in the tank, the bacteria have not yet established themselves to handle the bio load. In other words your tank is still cycling or the bacteria cannot handle the bio load.

Cardinals are very sensitive to higher ammonia and nitrite levels, especially over a extended period.​

The flashy colours of cardinals often provoke an attack from male bettas but their speed/agility and shoaling/schooling allows them to avoid the aggressor.

In your case the Cardinals may have been sick, which allowed the betta to get the better of them.

Most municipalities use chlorimines in their water supplies, if your detox agent only neutralises the chlorine part, your water-changes may even be contributing to the higher ammonia levels.

Use Seachem Prime to bind the ammonia and Seachem

Stability to cycle your tank.​

"Prime works by removing chlorine from the water and then binds with ammonia until it can be consumed by your biological filtration (chloramine minus chlorine = ammonia). The bond is not reversible and ammonia is still available for your bacteria to consume. Prime will not halt your cycling process."

but

Prime detoxifies ammonia, nitrites, and nitrates. It detoxifies these nitrogenous compounds by binding them into a non-toxic form. They stay bound for about 24-48 hours and then are released back into their original form.

Best to cut down on the feeding for the next week or so until your tank's bacteria can handle the bio-load.

More food = more poop = higher ammonia, the 30 second rule is a good baseline to use when feeding you fish.

Once your tank is properly cycled and ammonia level is at 0, you can slowly increase the bio load in the tank, hold off adding any new fish until then.

 

My water comes from a filter and I treat new water with Aquasafe plus (claims to neutralise chlorine and chloramine).

You could be right about the cycling though. I've been having complications with my initial cycle; I put the filter from my smaller cycled tank into the 20 gallon I'm using now. I hoped that would cycle the tank immediately (it didn't) so I introduced the cardinals. That was about 4 weeks ago and I've been doing water changes every 2-3 days as the ammonia levels were low, but never hit zero... Rookie mistake, yes, but I'm still pretty new to the hobby.

I'm off to the shops later today so I'll see if they've got some Seachem.

 

Ja, but at least I can say I'll never make the same mistake twice. I'm learning that there's a tremendous amount of trial and error in this hobby. The cardinal didn't make it.

Nitrite has been '0' for the past week, my nitrate readings have been around 0.1/0.2. The ammonia has never reached dangerous levels, according to the chart, but has never been '0'. I assumed that, since my fish weren't getting sick or dying, the ammonia was relatively safe, seems like even low ammonia readings are essentially a time-bomb. I ordered the Seachem, it'll arrive in 2 days.

 

What temp are you keeping the tank at? Apparently cardinals like the water pretty warm, around 27C

 

Good advice has been given and I think, that will get you sorted
Adding Stability is the main thing right now in order to build up the good bacteria and finish the cycle off
Follow the instructions carefully ( no water changes during the 7 day course of Stability)
Good luck, things will settle

 

Lets make that 8 days course xD
Day 1 @ 5 ml/40 lt
Days 2 to 8 @ 5 ml/80 lt

And remember to add 5 ml/80 lt after every major water change.

 

Have to agree with cardinals requiring warmer water - about 28C. The few pet stores i have observed keep them between 27 and 28.

 

Yes, the nitrate readings should be 1.0 not 0.1.
The readings on my API test kit chart list readings from 0 - 160ppm, however, the readings on my aquarium app (Aquarimate) list safe nitrate ranges as 0 - 0.2.
Obviously the app is incorrect, but I've been writing my readings down as decimals as the app has a nice chart timeline of parameters and using the apps albeit incorrect
decimal lets me make use of its chart.

UPDATE

I got a few things at the aquarium store and setup my little Betta tank, I dropped some flakes inside to raise the ammonia and jump start the cycle.
The Betta is housed inside a breeding net, in my main tank. He'll be there till his tank is FULLY cycled this time.

Best News: I tested the water this morning and my ammonia and nitrite readings have finally dropped to zero. The nitrates are at 10ppm, but I'm going
to give it a few more days before I do a water change, just to be extra sure that the cycle has completed. The shade of the net and the 10ppm nitrate is giving
me some pretty ugly brown algae, but that's ok, it'll be easy to clean off and stop once the net is gone.

Here's my beta's future home (30lit), I dropped in some flakes to introduce ammonia and jump-start the cycle.
I might get a snail or 2, if I can find one that my betta wont bother.