Mysterious Betta Death

[spankysalad]

I have a 10g tank which originally had 5 panda corys and a male betta. The other day i performed a routine daily water change as it's a reasonably new tank and it is still cycling. The fish were fine for about an hour afterwards and then they started acting differently. The pandas were all either upside down/on their sides on the bottom or just sitting there. They didn't react to any outside stimulus such as a moving finger past the tank or tapping on the glass, whereas usually they would shoot away. The betta was just floating up at the surface, only using its pectoral fins to move, and was just grasping on to one of my plants. I tested the water right away and all the values were at 0, seeing as it had only been about 30 minutes after the water change.

It's quite mysterious as i didn't do the water change any differently to how i have before. I made sure the temperature was equal and i used the water treater i've been using the whole time. I looked online and the symptoms seemed to suggest pH shock, but after a couple of days of testing the water coming out of my tap is only about 0.2 difference to the water in the tank after it has stood for a while.

Another problem is that a lot of things coincided with the situation. I had recently introduced about 20 malasian trumpet snails into the tank, but they had been in there for about 4 days and all of the fish fell ill within minutes of eachother. I have also been noticing blackish patches of sand which may have came to the surface whilst syphoning poo and food off the surface. I have heard they can be caused by anaerobic respiration? Could the disturbance have released something into the water? And finally about an hour before the water change my betta had experienced some minor fin loss, so i dosed a treatment of the fungus and fin rot medication from pets at home. Either way as soon as i noticed the ill fish i did another water change in case i had done something wrong.

I woke up the next morning to find the betta dead on the floor, but over the next 3 or 4 days the pandas have made a complete recovery and they are acting completely normal. Any suggestions about what could have caused this?

also, if it is some kind of bacterial infection, am i going to have to clean the tank before introducing new fish or will it be fine now the current fish have recovered?

 

[waterdrop]

Hi spankysalad and welcome to our freshwater beginners section!

So sorry to hear about the death of your betta. We all hate losing any of our fish but the ones with some individual character, like most bettas have, can hurt even more.

When fish are exposed to a cycling tank situation, its a matter of life and death to them. Its not a situation we like to see happen and is the reason we work hard in modern forums such as this one to explain fishless cycling to beginners and help them understand better the core skills surrounding the Nitrogen Cycle topic.

In your own case, you don't mention any numerical test results for ammonia, nitrite(NO2), pH or nitrate(NO3.) For most people who have been given good nitrogen cycle information, the ammonia and nitrite numbers are top in their mind. Have you got a good liquid-reagent based test kit that you've been using during the fish-in cycle?

We have lots of members who can help.

~~waterdrop~~