Mysterious deaths

[Mcgolg76]

My 20g tank has had a bunch of mysterious deaths this week.
Ammonia=0
Nitrites = 0
Nitrates about 10/15
Ph 7

Lost this week 2 pygmy Cory's, my remaining 2 panda Cory's. One cherry shrimp, a peacock gudgeon and most surprisingly my betas who was fine the night before. The major change I made was i replaced my substrate from gravel to pool filter sand. Did cause a mini cyle that only lasted two days. Also moved my black neons out and replaced with the pygmy Cory's two weeks ago. Both a pygmy and panda cory were acting sick before they died. All the fish in tank are acting super skittish. Generally a skittish tank to begin with. Confused by deaths. Heard that a change to sand could release ammonia pockets but it is coming up as zero. Any help would be appreciated

 

[Berylla]

From what I'm hearing, it sounds chemical.

I could be from the following:

1. The sand. I rinsed my sand until its no longer cloudy. And then I rinsed it more.

2. Forgot to add dechlorinator. It happens more than you think.

3. City water cleaned the system using elevated levels of chlorine and chloramine and overwhelmed you dechlor.

4. Something else that was added to the tank.

If you have been checking your water parameters, I don't think it's a mini-cycle.



FYI, I've been learning that Quikcrete pool sand could be too sharp for cories. All mine have died over time with them slowly loosing their barbels.

 

[Mcgolg76]

Don't think it is something in my water because I have three other tanks with zero deaths. Really don't think I forgot to add prime. If anything I might do a drop too much. Plus aren't shrimp very sensitive to that stuff. Have a huge colony with only one death. Also the first death was my beta. Aren't bettas a bit more tolerant to bad water conditions? For now only thing I know to do is just keep on doing water changes.

 

[Mcgolg76]

Oh and sand shouldn't be problem because I used from same 50lbs bag to change my 10 g tank.

 

[Berylla]

Hmmmm. I still think is chemical. Anything that fast if usually chemical. If it's bacterial, the fish look really bad - cloudy eyes, ulcers on skin, etc.

Very mysterious, especially just affecting the fish.

I agree, keep up with the water changes. You can also run carbon in your tank as a precaution.

I also suggest to use a carbon filter on your tap water to avoid city water issues. I run a 2 stage filter attached to my laundry sink to filter out chlorine, chemicals, rust, and even pathogens from the tap water.

 

[Mcgolg76]

Never use carbon but can't hurt. Fish don't really look sick. But just skittish

 

[Berylla]

I don't use carbon in my tanks either, but in this case, if there is a chance of a toxin in your tank, the carbon will soak it up.

I use the carbon filter on my tap to ensure that my fish get the cleanest water possible. When I change out my filters once every 3 months, they are exhausted - full of brown sludge.

 

[Delapool]

Was there any symptoms? Has ph been constant perhaps?

 

[Mcgolg76]

Constant ph. Saw the pygmy cory and panda cory lying on side before they died

 

[Cynic]

How much of the sand did you add at once? Sand in large amounts in relation to tank size can cause a sudden temperature drop which can stress and subsequently kill fish.

 

[Berylla]

Another thing that came to mind, stray voltage.

Stray voltage from a bad heater. Here is a youtube video showing you how to measure it in your tank.

[youtube]ffDctOPRS6c[/youtube]

 

[Mcgolg76]

About 30lbs and no deaths occurred till about 2 weeks after change

 

[Delapool]

Any other changes more recent? Pesticides around tank?

 

[tnfinfan]

Were the pygmy corydoras new arrivals or moved in from another healthy tank of yours? Wondering if you introduced sick fish? There are parasitic illnesses that can look like darting around and/or scratching.

 

[Sk3lly]

I think you can release massive amounts of methane gas when tearing out substrate. All the break down of waste under the gravel happens anaerobically (presence of no o2). I believe this produces methane gas which accumulates under the substrate. As you've removed the substrate you've released it into the water column. When i uproot plants in my sand substrate tank i can see the bubbles go up. I only do a few then wait a few days. Maybe worth researching online??

 

[tnfinfan]

Yes, there is a risk of stirring up nasties when removing substrate but you remove all the fish before you begin. And poisoning by toxic gas wouldn't have a two-week delay.

 

[Sk3lly]

Yes, there is a risk of stirring up nasties when removing substrate but you remove all the fish before you begin. And poisoning by toxic gas wouldn't have a two-week delay.

Seems more logical to me than some of the other suggestions. I was just putting the idea out there

 

[Mcgolg76]

Was pretty nasty when I removed the gravel. But all fish were out of tank and in the bucket when I removed the gravel. And after I emptied the tank completely wiped it out. No soap or any cleaners. Then two weeks later the betta died.

As for the pymy Cory's. I moved 8 from my ten gallon. Then the betta died. Then bought 5 more pygmies. Then rest of fish died. So it is possible the betta died from a different reason. Then got sick pygmies that got other fish sick. 4 of the next 5 fish that were all Cory's.

 

[absolutangel04]

Yes, it is quite possible that your new fish were the issue. Under the circumstances, it does not sound like it was your substrate change. The fish were removed during the substrate change, and then you have been checking your params with are fine. So, unfortunately, I vote that something came in with the new fish. Hopefully you have no more deaths!

 

[Mcgolg76]

Hopefully no more deaths when I get home from work