Impaired buoyancy & Erratic swimming resulting in death

[zephyr]

I purchased some lemon tetras about 2 wks ago and they didn't appear to acclimatise very well. 2 died within the first two days, and I associated it with stress as I assumed they died quickly as it happened overnight.
The other 3 were cautious but seemingly healthy, all with acceptable appetites and what not.
I purchased a pictus catfish about a wk and a half later for a friend who I'd give it to when he had a chance to see me (they're not always that easy to find here), it was only about 2-3 in long so I decided to put it in my tank 'til my friend could get it.
Unfortunately it just seemed to pass away, the fish store I bought it from didn't seem that clean and the water it came in was rather dirty looking. I assume it may not have been very healthy when I got it. It also didn't seem to eat any blood worms I tried to feed to it.
After it died my remaining lemon tetras started to die.
They'd get strange buoyancy problems where they'd scoot around with their tails in the air, upside-down and extremely erratically, as if they were scratching themselves or in pain or something. All three have died now.
There is a betta in there too who hasn't seemed to be affected.
I'm not really sure whats going on as I haven't dealt with much fish pathology except for ich??
Any help would be greatly appreciated!!!

Jus.

 

[Karegg]

Can you post your water parameters? Ammonia, nitrites, nitrates, pH, etc?

 

[Fishyfanatic]

Your water parameters will definitely shed light on the situation. How long has the tank been set up? What size is it? Have you done any major cleaning lately on the tank?

 

[zephyr]

I don't have any ammonia/nitrite/nitrate kits as they tend to be too expensive and I'm a student on a budget. The pH is somewhere around 7.5-7.8, not sure of the dH.
The tank's only new, its been set up for just over 7 weeks now, but the betta is fine so that what has made me not question that the tank has cycled. I used a prawn to initiate the cycling process.
I tank is what I believe is 10 g, although we use metric units here. Round about there anyway.
Now you mention it, with any major cleaning, I had a piece of wood in there I purchased from a fish store and had been soaking. I put it in the tank a bit too prematurely and there were still tannins leaching into the water, so I removed it. I also did a rather drastic water change as the water was very discoloured. I did this the day before I purchased the tetras. Do you think this may have been detrimental?

 

[Fishyfanatic]

Until you have a test kit, it is all a guessing game. Take a water sample to your lfs and ask them to test it with a liquid reagent test kit. Your loss of fish and having to drive to the lfs to have the water tested will end up costing more than the test kit.

The tank is probably not cycled. Unless you tested the water to ensure the cycle has completed, you can't be for sure. When you did the water change, did you clean the filter or do a deep gravel vac? Removing the wood and doing a large water change shouldn't be a big deal as long as you didn't disturb the bacteria in the gravel and in the filter. The tank needs to mature a bit longer before doing any drastic cleanings. Simple water changes won't do harm though.

Get the water tested and we can point you in the right direction. If all is clear and the tank is cycled (0 Ammonia and Nitrites with 10+ Nitrates) we can go from there. BUt if it itsn't, we can take appropriate steps with water changes.