Mysterious Fish Deaths.

[Aquella]

Hello all. I hope someone can help me.

The fish in one of my aquariums, a 29 gallon, established for about 10 years, have been dropping like flies.
I have lost so far, in the last week:
5 female Bettas. (All.)
1 Cherry Barb. (Of 3.)
2 Pygmy Corys. (Of 6.)
4 Yellow Neons. (Of 5, these were added most recently, a little over a month ago. They were tiny, 1/4" or so.) I'm actually not certain that these died for the same reason. They may have been eaten. I never found bodies.

I have to assume that whatever the problem is, it was introduced by the Yellow Neons.
I do not believe that the problem is due to my Nitrates, as none of the other setups are having any troubles, and there are no signs of Nitrate poisoning.

Left in the tank I have:
2 Bristlenose Plecos.
4 Pygmy Corys.
2 Cherry Barbs.
Various Snails
Amano and Cherry Shrimp.
(I have not lost any shrimp or snails.)

All of the fish besides the Yellow neons are between 2 and 7 years old.

None of the fish that have died have had any sign of illness, disease, or any other physical abnormality.
All of the fish look perfect, just dead.
All of the fish are behaving normally, brightly colored, eat well, etc. No gasping, rapid gill movement, constipation issues, clamped fins, or abnormal behavior of any kind.
I can’t stress enough how perfect everything seems, and then a few hours later, usually in the morning, there’s a dead fish or three. Perfect looking, brightly colored, fully intact, not a scratch on them, dead fish.

My Nitrites and Ammonia are 0.
Nitrates at 40-60ppm. I realize this is high, they’re at this reading straight out of the tap. We're working on getting the issue resolved.
PH is at 7.6

We use only natural products in our home.
No new products have been used. Nothing has fallen into the aquarium water.
No new plants/decorations/anything has been added recently.

This is one of 6 aquariums I currently have running. The others are a 75 gallon community, 30 gallon Angelfish grow-out, 15 gallon Celestial Pearl Danios/Betta, and 2 5 gallon Betta.
All of my aquariums have the same water and parameters. No deaths in any of the other setups.
All aquariums are heavily planted, all plants are healthy.
I’ve been performing partial water changes. I have not added any meds, as I can’t imagine what I’d be treating for.

So, what’s going on? And more importantly, how do I fix it?

Thank you very much for any suggestions.

[fisherman]

My Nitrites and Ammonia are 0.
Nitrates at 40-60ppm. I realize this is high, they’re at this reading straight out of the tap. We're working on getting the issue resolved.
PH is at 7.6

i dont think it suposed to be that high straight out the tap??? couldnt that be dangerous to drink?? and i thought 30ppm is the most you would want it befor a w/c??

[fisherman]

My Nitrites and Ammonia are 0.
Nitrates at 40-60ppm. I realize this is high, they’re at this reading straight out of the tap. We're working on getting the issue resolved.
PH is at 7.6

i dont think it suposed to be that high straight out the tap??? couldnt that be dangerous to drink?? and i thought 30ppm is the most you would want it befor a w/c??

[darb]

First check to make sure that your test kits haven't expired. I have never bothered to test the tap water, but yes, MV water shouldn't be reading 60 out of the tap.

[darb]

OK forget my previous post, New York they very well could be at 60 straight out of the tap along with countless other chemicals ...

What percentage are you doing for water changes, typically you should be doing a minimum of 25%.

[Tsunami28]

If your tank has been set up for ten years have you ever done a thorough stirring of the substrate? There may be possible pockets of gas in there that may have escaped and killed your fish.

[rescuepenguin]

My first thought was "old tank syndrome".

I would take a sample of your tank water to a fish store for a second opinion of the parameters, even if they charge you a dollar or two it is worth it.

Going back to my first thought, how often to you vacuum your substrate?

Steve

[oakley1984]

dont quote me on this or anything, but im fairly positive that after about 40ppm nitrates its not necessarily you'll get nitrate poisoning... but it compromises the fish's immune system to the point it no longer functions, at which point introducing a new fish that may have a sickness... there's nothing stopping it from spreading like wildfire in your tank. so if your nitrates are coming out of the tap that high chances are this has been a continuing problem, since it was a closed system with no foreign bacteria introduced (until adding your yellow neons), that after adding them youve disrupted their shall we say equilibrium. so from my personal point of view its an unfortunate unforeseen accident due to the listed circumstances... hope this helps !