Am I killing my Black Widows?

[Quatermass]

I've a 60l 24" wide Rena tank which is 3 months old and contains lots
of plants, a 1 week old eheim 2210 filter alongside the rena II
internal filter and about 15 fish, 3 dwarf african frogs, 3 golden
apple snails. Water as clear as crystal.

My shoal of 4 young black widow tetras (Gymnocorymbus ternetzi), bought
about 4 weeks ago from a local petshop have started dying on me at a
rate of about 1 a week now. I've got one left.

Water pH is 7.4, saline is 1.004. Nitrates is less than 15 with
Nitrites, ammonnia at zero, gH is about 20 and temperature is 24C.
I do a 10l water change once a week.

The black widows seem to lose all control of their swimming and just
spend their last few hours floating with the current on their side and
are clearly still breathing. Every now and then they try to swim again
for a few secs and then stop. They take about 3 hours to die.

All the other fish, young marble angelfish, 3x dwarf gourami, 2x
mollies, 1x golden gourami, 4x indian glassy fish, 2 bronze corys and 2
Khuli loaches and wee frogs seem to be doing very well and get on
together.

The currently surviving BW is actually the smallest one.

It may only be a coincidence but, I only noticed the last 2 dying black
widows when I put my hand in to add a new plant.

So I have to ask did I frighten all my BW to death?
As I'm new to this hobby I'd appreciate some advice.

[Billy]

"Quatermass" > wrote in message
oups.com...
|
| Water pH is 7.4, saline is 1.004. Nitrates is less than 15 with


Saline is 1.004? Why are you testing for salinity in a freshwater
tank? Do you add salt? That might be the problem right there, tetras
are not fond of salt, and do not tolerate it very much in the water
at all.

[Limnophile]

"Billy" > wrote in message
...
>
>
> "Quatermass" > wrote in message
> oups.com...
> |
> | Water pH is 7.4, saline is 1.004. Nitrates is less than 15 with
>
>
> Saline is 1.004? Why are you testing for salinity in a freshwater
> tank? Do you add salt? That might be the problem right there, tetras
> are not fond of salt, and do not tolerate it very much in the water
> at all.

Salt will cause balance problems, not to mention osmotic distress.
Do twice daily 20-30 percent water changes for 3-4 days to remove the salt.

If salt isn't the problem, it's probably a bacterial infection of the swim
bladder or nervous system. Food treated weith antibiotics may help, but the
majority of fish with balance problems die anyway.

Limnophile

[Quatermass]

I put a wee bit of salt in because it's a good tonic for freshwater
fish and I've got mollies and Indian Glassy fish which prefer a bit of
brackish water.

I mean its only 1.004, hardly any at all.

[Billy]

"Quatermass" > wrote in message
oups.com...
|I put a wee bit of salt in because it's a good tonic for freshwater
| fish and I've got mollies and Indian Glassy fish which prefer a bit
of
| brackish water.
|
| I mean its only 1.004, hardly any at all.

<shrug> It's still a possibility. Mollies can actually be adapted to
sal****er, (1.023-24) while tetra's do not tolerate salt at all. In
your position, I would cease the salt treatment until I could set up
another tank so these fish with different needs can be cared for the
way they prefer.

[Quatermass]

I not read anywhere that BW can't tolerate a little salt. All fish on
this planet has salt in their bodies.
I've read that osmotic stress can be reduced by adding a little salt in
the surrounding water as it reduces the amount of work their kidneys
do.

But I will heed your advice and reduce the salt in my tank. :-)