Why Do My Fish Keep Dying? Lack Of Oxygen?

[Benedict0]

I'm very new to owning fish and I seem to have failed at the first hurdle as my first group of harlequin rarbrosas in my newlying set up aquarium have all sadly passed away.

About a week ago I bought a second hand 40l (10 gallon) fish tank which came with a filter, heater and declorinate. I set up the tank with gravel, various ornaments and 2 live plants. After 48 hours of running the tank I took a water sample to my local aquatic store to check but came back fine. The associate said the water water was safe for fish so I bought 6 harlequin rarbrosas.
The fish seemed fine for the first 24 hours but after that I noticed some of the fish staying at the top of the water as if they were gasping for air. The next day the fish were still doing this so I did a 10 % water change. The fish seemed okay for an hour or so but they started swimming to the surface again. Shortly after, one of the fishes died. After I removed the fish I took a water sample to the aquatic centre which didnt show any problems. The assistant advised me to buy an air stone to help get more oxygen into the tank (which I did). Then when I came back from the store another fish had died. After setting up the stone and running it, the rest of my fish slowly started to die one by one. The water seemed fine and the fish looked healthy but I can't figure out what I was doing wrong. As the fish were dying they would swim in circles rolling over.

There are a few factors which I think may have played a part:
There was a heatwave during the time I had the fish and the temperature was around 28°c which is slightly above the green mark on my thermometer.
I didn't sterilise the filter and heater before using.
When setting up the tank the only fluid I used besides water was the declorinate.

Does anyone have any idea of what could have caused the fish to die or what I could do next before getting more fish?
Thank you!

 

[Ch4rlie]

Hmm, it looks unfortunate but seems that you may not have cycled your tank and filter first before adding the fish.
 
Basically means there is no bacterias to deal with ammonia that the waste and respiration from fish produces.
 
I would suggest you may find it useful to have a read of the fishless cycling article, will explain things in more details and also gives a guideline to do a fishless cycle on your tank and filter.
 
http/www.fishforums.net/index.php?/topic/421488-cycling-your-new-fresh-water-tank-read-this-first

 

[fluttermoth]

I'd just like to add, to Ch4rlie's good advice, that ammonia and particularly nitrite, chemically bind to the fish's blood, preventing them from taking up oxygen, which is what makes them gasp at the surface; it's not because there's not enough oxygen in the water.

 

[AshGillott]

Hi, sorry to hear your bad news.
I set my tank up like you did yours and the fish shop (after taking a water sample in) told me to get some fish in there quick, so I did..
The difference between me and you is that I knew it was too soon as the tank cycle wasn't complete so I was doing 30% water changes every day for a week or more then every 2 days after that and occasionally a 50% change as opposed to the 30%.
If you read the link above it says it will take weeks to cycle a tank properly before it's ready.
Fortunately mine is now done and dusted and in 4 weeks I have only lost 2 fish a male guppy which died 2 days ago (probably from old age I think) and a male platy which I believe was a parasite infection which caused him to balloon.
Apparently Platies are a very good fish to start cycling your tank with because they are hard as nails?


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[Ch4rlie]

Fortunately mine is now done and dusted and in 4 weeks I have only lost 2 fish a male guppy which died 2 days ago (probably from old age I think) and a male platy which I believe was a parasite infection which caused him to balloon.
Apparently Platies are a very good fish to start cycling your tank with because they are hard as nails?

 
Four weeks to complete a fish in cycle is actually very fast indeed, I wonder if you added any mature media or bottled bacs in order to speed up the cycling process?
 
But either way, fish in cycling is hard work in terms of the amount of water changes and testing that is required and to complete in 4 weeks while only losing 2 fish is no mean feat.
 
There are no real good fish for fish in cycles to be entirely honest, its basically just either luck or to the fishkeeper being very meticulous with water changes and testings.
 
Regardless of AshGillots success with his fish in cycling, I would never recommend a fish in cycle due to the simple fact its not neccessary as getting ammonia and lots of informationa nad advice being available here on this forum.
Also fishless cycling is always best, becuase if any mistakes are made, no fish will suffer for it. Believe me, its much less stressful doing a fishless cycle

 

[AshGillott]

Being a newbie you goto the shop with your water and listen to the shop people, they say put it in and you do.
I just looked at the dates and it's almost 6 weeks actually but it was a lot of messing around and using gallons and gallons of water in the process.
It is also a moderately heavy planted tank so maybe that helped a lot too.
Either way it's done and now I have another tank of fry which surprisingly survived for a few days in the community tank before I obtained another one to put them in


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