The tank is either cursed, or I'm a fish serial killer...

[Eldachleich]

Out of all my various bowl and tanks and tub pond only this one suffers.
I'm not sure why. And its getting to the point where I'm afraid to stock it ever again.
My 6.6 gallon is... killing fish.
Literally. One day they are they. I wake up the next day any they are gone. Just gone.
And its always the same story. I buy them in great health. I put them in the tank. They last anywhere from 2 - 4 weeks. And within an hour they vanish.
All the while swimming, behaving, eating normally.
They vanish, I panic. Check everything. Test all the levels. Nothings every wrong.

Any idea on whats happening?

Tank stats..
Temp 77 - 80
Ammonia - 0
Nitrites - 0
Nitrates - 0
pH - 7.5
Substrate - MGOPS capped with black sand
Filtration - Aquaclear 20 and Marina Slim S15

I dont have a a TDS or GH or Kh test kit. But I plan on getting one soon.

I'm going to assume they are all high since... well.. Our tap water is hard.

The filters all have presponges and there isnt anything toxic in the tank. All it has is crypts mopani wood lace rock and sand. There is also a cover on the top so they arent jumping...
The tank has been set up for a year, its well cycled. Been tested by multiple calibrated test kits.

Another thing. My tap water comes out at 8.2 but after a few hours circulating in the tank its becomes 7.5.. I think.. When I test with the high pH kit it registers me at the lowest end. And with the low pH kit it registers at the highest end. So since they max out at 7.6 and 7.4 I'm assuming around 7.4.
I've recently taken to letting it sit with an airstone overnight and then taking the airstone out a few hours before the waterchange.
Will that actually help anything? Could the pH swing form it degassing be what was killing them?
Or was it something else.
I love this tank so much. And I'm really enjoying scaping it and watching it grow. But my fish all dying is sort of deterring me from.. Continuing.

This trend has been happening for about... 3 months now.

[AirstoND]

I've noticed you've had local rocks in your tank.

1) Was this done a significantly long time before adding fish? Sterilizing method? You might have introduced parasites or toxic pesticides from runoff.

2) Are all your fish from same LFS? You make no mention of which fish are dying.

3) Why are you removing the airstone from the tank instead of just turning off?

4) Do your fish have lesions/visible diseases? Or are they just floating around dead?

[PlantedRich]

When you say there is nothing toxic in the tank, I wonder. Do you know the history of this tank so that you can be assured it was not cleaned with a toxic item? Acid Majic is the name of a cleaning solution which is great for removing hard water buildup. It is also extremely hard to rinse off if it gets in around trim. It is also very likely to kill fish!

You understand how a tank and filter may need to cycle?

Just a thought.

[FriendsNotFood]

I have the same water issue as you do. The pH comes out of the tap at 8 and my tank pH is 7.4. I've taken to not doing water changes anymore because when I used to do large ones I would lose fish. A few of my green neons would turn white after water changes. Now that I don't really do them anymore I haven't seen any more white neons. I think the trick is really, really small water changes, and more of them if you have to.

[Diana]

Friends and Eldachleich:
Run some tap water into a glass.
Test pH right out of the tap.
Let the glass sit out 24-48 hours.
Test pH.

Highly likely what is happening:
There are dissolved gasses in water.
Some water does not have as much gas as the air. (Especially well water)
When such water is exposed to the air it gains gases, especially CO2.
Adding CO2 to the water drops the pH.

I do not know if this is killing the fish, but it could be.
Running a bubbler or small pump in the water overnight will help. By circulating the water you are allowing it to adsorb all the gases it can so it will have the same level of gases as the tank water. (This is a good time to add minerals if needed, dechlor, or filter the water through peat moss, or any other treatment it needs, too)

I have sort of the opposite problem. My tap water already has gases in it, and holds more gases in the cold weather, and this causes problems for my fish. I have lost some after doing a direct fill after a water change. I also fill a barrel and circulate the water overnight to make it safe for the fish. But in my case the excess gases are leaving the water.

Other than that, you can test each item in the tank separately, by placing it in a container that just has water (perhaps from another tank that does not kill fish) and a fish. For example, test the rock from the suspicious tank, a handful of substrate, the ceramic mer-person and so on. Test each item separately.
If you find that something from that tank is killing the fish I would suggest thoroughly cleaning the tank, perhaps new substrate, in hopes of removing any lingering traces of whatever is killing the fish.

[Eldachleich]

I've noticed you've had local rocks in your tank.

1) Was this done a significantly long time before adding fish? Sterilizing method? You might have introduced parasites or toxic pesticides from runoff

The rocks are from my yard, have been in the yard close to 40 years. My yard always has been and will be organic. Originally they are from a local bhuddist temple thats also organic. I believe they got the rocks from a river in the mountain. No pesticides or chemicals near them in a long time.
They were boiled for a few hours and set in a bleach solution overnight.
I used them in another tank for at least 4 months with great success. And several other ones before that. Proven fish safe.

2) Are all your fish from same LFS? You make no mention of which fish are dying.

The fish are from various sources. Two different LFS and 3 different online sources. Plus a few random other fish stores along the way.

3) Why are you removing the airstone from the tank instead of just turning off?

The airstone doesnt go in my tank. It goes in the container thats holding the water for my waterchange. I take it out after I'm done.

4) Do your fish have lesions/visible diseases? Or are they just floating around dead?

No visible lesions, no marks. Perfectly happy healthy active fish. Every time.
And they don't float around dead. In fact I've never found a body. Not once.

[Eldachleich]

Originally Posted by PlantedRich

When you say there is nothing toxic in the tank, I wonder. Do you know the history of this tank so that you can be assured it was not cleaned with a toxic item? Acid Majic is the name of a cleaning solution which is great for removing hard water buildup. It is also extremely hard to rinse off if it gets in around trim. It is also very likely to kill fish!

You understand how a tank and filter may need to cycle?

Just a thought.

Bought brand new from Petco.
Been mine since day one.
And yes. I do know the cycle. I have two well cycled filters on this tank. Its been cycled for a year now.

[Eldachleich]

Originally Posted by FriendsNotFood

I have the same water issue as you do. The pH comes out of the tap at 8 and my tank pH is 7.4. I've taken to not doing water changes anymore because when I used to do large ones I would lose fish. A few of my green neons would turn white after water changes. Now that I don't really do them anymore I haven't seen any more white neons. I think the trick is really, really small water changes, and more of them if you have to.

Everyone always got active in my tanks after a waterchange. But I suspect that my new regime of letting it degas overnight might help.
I'm gonna try your method for a while and see if it helps.

[Eldachleich]

Originally Posted by Diana

Friends and Eldachleich:
Run some tap water into a glass.
Test pH right out of the tap.
Let the glass sit out 24-48 hours.
Test pH.

Highly likely what is happening:
There are dissolved gasses in water.
Some water does not have as much gas as the air. (Especially well water)
When such water is exposed to the air it gains gases, especially CO2.
Adding CO2 to the water drops the pH.

I do not know if this is killing the fish, but it could be.
Running a bubbler or small pump in the water overnight will help. By circulating the water you are allowing it to adsorb all the gases it can so it will have the same level of gases as the tank water. (This is a good time to add minerals if needed, dechlor, or filter the water through peat moss, or any other treatment it needs, too)

I have sort of the opposite problem. My tap water already has gases in it, and holds more gases in the cold weather, and this causes problems for my fish. I have lost some after doing a direct fill after a water change. I also fill a barrel and circulate the water overnight to make it safe for the fish. But in my case the excess gases are leaving the water.

Other than that, you can test each item in the tank separately, by placing it in a container that just has water (perhaps from another tank that does not kill fish) and a fish. For example, test the rock from the suspicious tank, a handful of substrate, the ceramic mer-person and so on. Test each item separately.
If you find that something from that tank is killing the fish I would suggest thoroughly cleaning the tank, perhaps new substrate, in hopes of removing any lingering traces of whatever is killing the fish.

Already done that test.
It comes out the tap at 8.2 and degasses to 7.5 within a few hours. And it stays at 7.5.
I'm hoping the airstone thing will help alot..

I've already tested each component seperatly. And am using the same components in different tanks with no ill effects. Some of everything in the tank is spread throughout my house.

[Kitsune_Gem]

Perhaps you have some critter in your tank that has gone unseen that's killing and eating your fish, thus leaving you no dead body to find..

[Eldachleich]

Originally Posted by Kitsune_Gem

Perhaps you have some critter in your tank that has gone unseen that's killing and eating your fish, thus leaving you no dead body to find..

I did think of that...
After the last few fish I chanced died I did a thorough sweep of the tank and found nothing.

[catg]

This reminds me of a creepy article I read a while back about an aquarium place that was having trouble with one of their marine tanks. They had fish disappear, had fish with big chunks taken out, had corals with big chunks taken out etc. From what I remember, they thoroughly cleaned the tank several times to try to figure out/fix what was going on. It wasn't until they gave up and totally dismantled the tank that they found a 4 foot long marine worm hiding in the substrate. It was a very nasty looking thing - had a big round mouth with teeth all the way around, and stinging bristles all along it's body that caused paralysis. Somehow, it managed to escape detection until the tank was emptied.

Cat

[josolanes]

If you're not finding bodies either something is definitely very odd. I'd tear the tank down completely and consider a new substrate to ensure there's nothing in the substrate (or at least sift through the substrate)

Otherwise, no fish found around the tank? (jumping the tank)

The bodies *have* to be going somewhere....

[Kitsune_Gem]

Originally Posted by catg

This reminds me of a creepy article I read a while back about an aquarium place that was having trouble with one of their marine tanks. They had fish disappear, had fish with big chunks taken out, had corals with big chunks taken out etc. From what I remember, they thoroughly cleaned the tank several times to try to figure out/fix what was going on. It wasn't until they gave up and totally dismantled the tank that they found a 4 foot long marine worm hiding in the substrate. It was a very nasty looking thing - had a big round mouth with teeth all the way around, and stinging bristles all along it's body that caused paralysis. Somehow, it managed to escape detection until the tank was emptied.

Cat

eunice worm

Nasty nasty hitch hikers, a reefers worst nightmare imo. They hide in the sand, and normally only come out at night. Most reefers have deep sand beds, and are not shinning flash lights into their tank at 2 am to see whats crawling around in there. I am sure theres got to be something similar in fresh water *Shiver* Ive seen reefers pull out 4 foot one once.. They can grow up to 9 feet..

[josolanes]

Originally Posted by Kitsune_Gem

eunice worm

Nasty nasty hitch hikers, a reefers worst nightmare imo. They hide in the sand, and normally only come out at night. Most reefers have deep sand beds, and are not shinning flash lights into their tank at 2 am to see whats crawling around in there. I am sure theres got to be something similar in fresh water *Shiver* Ive seen reefers pull out 4 foot one once.. They can grow up to 9 feet..

Omg!

I know I've also heard of mantis shrimp getting into reef tanks through live rock (with a random loud "pop" at nights)