Mystery fish loss

[TriBeCa]

Hi all. My 46 gal. bowfront has been going along fairly smoothly for a month or two now. Tanks been cycled, water quality good, 20% water changes weekly, no sign of disease or parasites.

Inhabitants: 6 rosy barbs, 3 black lyretail mollies, 3 clown loaches, all ~1.5 - 2.5"

A couple days ago I noticed one of the loaches was in really rough shape. His swimming seems laboured compared to the other loaches, and he often just rests on the bottom of the tank (when he's not hiding in the cave all 3 loaches have claimed as their own). I can see some kind of white-ish discoloration inside him, that runs from his head almost down to his tail. It is only visible under his orange coloration, not the black, so it's not external. As I said, no sign of parasites, though he does sometimes scrape his body against the driftwood and substrate.

At any rate, he's still hanging in there, although I almost euthenized him a couple nights ago (he perked up after 15 minutes or so - I thought he was done for). But today I found one of the female mollies pressed up against the filter intake, clearly dead. No sign of physical damage. Some strange white blotch on its face, on the intake side (not sure if this could have been due to the water flow into the filter, or if it was there before it died). I hadn't noticed any strange behavior from the mollies, and the other two seem fine.

Any suggestions on what might be going on?

The only other thing that might be relevant is that I lost a rainbow shark in this tank about 3 weeks ago. He'd been getting more and more reclusive for days, and then when I realized I hadn't seen him for a couple days I went searching through the tank ornaments. I turned up about 25% of his torso in the loach cave, and what was left of him had turned totally white.

[Dave66]

Hi all. My 46 gal. bowfront has been going along fairly smoothly for a month or two now. Tanks been cycled, water quality good, 20% water changes weekly, no sign of disease or parasites.

Inhabitants: 6 rosy barbs, 3 black lyretail mollies, 3 clown loaches, all ~1.5 - 2.5"

A couple days ago I noticed one of the loaches was in really rough shape. His swimming seems laboured compared to the other loaches, and he often just rests on the bottom of the tank (when he's not hiding in the cave all 3 loaches have claimed as their own). I can see some kind of white-ish discoloration inside him, that runs from his head almost down to his tail. It is only visible under his orange coloration, not the black, so it's not external. As I said, no sign of parasites, though he does sometimes scrape his body against the driftwood and substrate.

At any rate, he's still hanging in there, although I almost euthenized him a couple nights ago (he perked up after 15 minutes or so - I thought he was done for). But today I found one of the female mollies pressed up against the filter intake, clearly dead. No sign of physical damage. Some strange white blotch on its face, on the intake side (not sure if this could have been due to the water flow into the filter, or if it was there before it died). I hadn't noticed any strange behavior from the mollies, and the other two seem fine.

Any suggestions on what might be going on?

The only other thing that might be relevant is that I lost a rainbow shark in this tank about 3 weeks ago. He'd been getting more and more reclusive for days, and then when I realized I hadn't seen him for a couple days I went searching through the tank ornaments. I turned up about 25% of his torso in the loach cave, and what was left of him had turned totally white.

Sounds like there's some sort of toxin in your tank. Any kind of metals in contact with the water? Have plastic ornaments? Any damp wires near it? The water conducts electricity well, and causes all kinds of fish problems.
The white from your shark and mollie is just the start of decay of a dead fish. The loaches were just cleaning up.
When you say water quality is fine, you mean ammonia 0, nitrite 0 and nitrate less than 10 ppm, right?
Is the whitish mark along the lateral line of that loach?

Dave

[TriBeCa]

Yeah, WQ just as you described. Sometimes nitrates creep into the 10-15 ppm range, but never higher. The line on the loach is along both sides of his long axis, yes.

There are three ornaments that I'm not sure exactly what they're made of. Got 'em at petco, and you see them all over. It might be plastic, but they've been in the tank since before there were any fish.

No wires in the tank except the one coming out of the submersible heater. There's also the tube for the air pump.

Finally, I treat the tank with a water conditioner (for chlorine, cloramine, and heavy metals) after every WC.

[Dave66]

Yeah, WQ just as you described. Sometimes nitrates creep into the 10-15 ppm range, but never higher. The line on the loach is along both sides of his long axis, yes.

There are three ornaments that I'm not sure exactly what they're made of. Got 'em at petco, and you see them all over. It might be plastic, but they've been in the tank since before there were any fish.

No wires in the tank except the one coming out of the submersible heater. There's also the tube for the air pump.

Finally, I treat the tank with a water conditioner (for chlorine, cloramine, and heavy metals) after every WC.

Reason I asked about the plastic ornaments as the plastic can have mold release agents on them. Those agents keep the plastic from sticking to the molds used to make the product. I've heard of people losing fish as you have with plastic plants in the tank.
All plastic ornaments should be washed with dishwashing soap and water, rinsed very thoroughly, then completly dried before use.
I know many people use water conditioners after they've put the water in the tank during water changes and have problems. I know the water treatment claims to instantly eradicate the substances but don't believe the packaging. It takes several minutes before the chloramine bond is broken between the chlorine and ammonia. Water companies use chloramines because its much more stable than just Chlorine, and thus more difficult for water treatments to break that bond.
As you've probably figured, when you put your water treatment in your tank, you're liberating free ammonia in there. If I remember correctly, its inorganic ammonia, so hobby test kits can't detect it. Your fish can, though.
I store water changing water in clean Rubbermaid trashcans. I use a Python to remove the old water, but I pump the new water from the cans.

Dave

[TriBeCa]

Hmmm.... Any advice on how I can put only pre-treated water back in the tank in a 500 sq. ft. manhattan apartment with only one 5 gal. bucket? Should I just change one bucketful at a time? How long should I let the conditioned water sit before putting it in the tank?

Also re: the ornaments - no plastic plants, just caves. Is it worth taking them out to wash them (they've been in there for almost 2 months now)? It'll piss the loaches off to no end to not have their cave anymore, I'm sure.

[Dave66]

Hmmm.... Any advice on how I can put only pre-treated water back in the tank in a 500 sq. ft. manhattan apartment with only one 5 gal. bucket? Should I just change one bucketful at a time? How long should I let the conditioned water sit before putting it in the tank?

Also re: the ornaments - no plastic plants, just caves. Is it worth taking them out to wash them (they've been in there for almost 2 months now)? It'll piss the loaches off to no end to not have their cave anymore, I'm sure.

LoL I had a pair of 30's and a 10 gallon in my little old dorm room in college. I kept the trashcan in the closet.
I use well water, but I treat it the same way you do. I have to mix my tap with water from my RO/DI units to keep the fish that I do, but I store the mixture in the cans at least 24 hours before use.
I use a little mag drive pump to replace the clean water in the tanks. I aireate the stored water for a few hours before using it to outgas the liberated chlorines and ammonias.
It's gonna take some continued detective work to figure out why your fish are dying. The shark you had is very hardy. Mollies are always a bit touchy without being in a brackish tank. They often go belliy up in pure freshwater in newer tanks. Remember, mollies can be kept in marine tanks; they like the salt. The other fish you have do better without it.

Dave