Mysterious repeated fish deaths

[rootbeer]

I would be grateful if anyone could shed some light on the problem I've been having.

In both of my tanks, fish will suddenly die with almost no warning signs. It only happens to one, maybe two at a time while the others seem perfectly healthy, and the fish that die show no outward symptoms of disease and I haven't been able to spot anything after removing them from the tanks. They'll be fine for weeks on end, and then one will die overnight.

Both tanks are fully cycled, pH is neutral, I have no notable algae problem, and I do frequent partial water changes. There's no overcrowding, in fact I keep them very sparsely stocked (even more so now that they have been dying ). One tank is a heated tank that I keep rosy barbs and bala sharks in, the other is a larger cool tank that I keep small comet goldfish in.

I've tried everything I can think of: extensive tank cleanings, bought new dechlorinator and water conditioner, changed foods, added aquarium salts, but they keep dying one by one and only show signs hours before they die. The only symptoms I've noticed are mild discoloration and they'll hide or lie on the bottom or lean against the pump when they're about to die.

I've never had this problem before, and only happened when I moved into a new place, but this doesn't sound like heavy metal poisoning to me or anything environmental. Honestly, I'm at a loss as to how it can be happening in both tanks simultaneously with the same pattern - does anyone have any thoughts at all? Thanks!

[jerseybird97]

you said all parameters are optimal? Nitrates and such. If both your tanks are experiancing the same problem my question is what is the correlation between the 2 tanks? Have you put something from one into the other? Let us know about parameters and maybe a mod or someone else will have some input.

[EscVelocity]

Could be parasitic. You could treat for parasites as a precaution, or disect and inspect the insides of your next death for worms, gill flukes, ect....

Have you added new fish or plants to the tank since you have moved?

[rootbeer]

All parameters are pretty much perfect in both tanks Nitrates/Nitrites/Ammonia/pH, all good. I've thought a lot about the connection between the two tanks - the only common factors are (a) same water source, and (b) same chemicals (dechlorinator/conditioner/salt). Nothing has been exchanged from one to the other tank at any time.

No new plants have been added. I have added fish as the fish have been dying, but I didn't add fish before this started.

I have a dead bala shark today (hence my posting this question), so I'll look with a loupe to see if I can spot anything at all.

Thanks for your thoughts on this!

[jerseybird97]

How long has the tanks been in use?

[mfdrookie516]

what are the actual readings on the ammonia, nitrite, and nitrate?

[ezy33]

Are you treating the new water for Chloramines & Chlorine before adding to the tank? Do you have a ammonia test kit?

[rootbeer]

To answer the above questions:
- Actual readings from both tanks: Ammonia: <.25 ppm, Nitrate 10-20ppm, Nitrite 0-0.05ppm, soft water ~75 ppm, chlorine/chloramine 0, alkalinity is a bit low at ~80-100 ppm, pH ~7.
- Both tanks are about a year old, started fresh when I moved into my new place. No problems until about 2-3 months ago, but nothing of note occurred before the fish started dying.
- Yes, I do treat for chlorine/chloramine with Amquel+ and use NovAqua+ and a small amount of aquarium salt at water changes.

[spoonman]

Ammonia and Nitrite should be 0, not about 0. Although I think the numbers that you are showing dont seem deadly. I would bet if you think about it you are sharing things between the tanks, like nets, python for water changes, buckets.....etc. Might want to look at cleaning all that stuff with bleach and water then let it dry and rinse with water and dechlorinator mixed 4x the normal amount.

[joy13]

Why are you adding salt? You might consider there might be a build up of salt, salt doesn't evaporate.