Dying Cory Fish

[RJLB119]

pH: ~7.6
ammonia: 0
nitrite: 0
nitrate: <20
kH: ???
gH: ???
tank temp: 80deg F

Fish Symptoms (include full description including lesion, color, location, fish behavior): Nothing strange!  They were swimming happily Sunday, as usual.  I came home to 1 dead one Monday night and a second dead one Tuesday.  The third is just hanging on the bottom not moving today (Wednesday).

Volume and Frequency of water changes: 10 gallon, 2 gallon water changes every Sunday.  Except this Sunday, I was going to do it Monday.  Then saw the dead fish.  Changed Tuesday.

Chemical Additives or Media in your tank: pH salt to bring down (1 tiny pinch 2 weeks ago)

Tank inhabitants: Had 3 frogs, but they have died.  3 cories, but 2 have died.  Only 1 cory in the tank.

Recent additions to your tank (living or decoration): Nothing!!!

Exposure to chemicals: None
 
I have been to the fish store multiple times.  I am new to this, and have done everything slowly.  The plants are living.  My nitrates are very low.  I had the levels all checked at the store yesterday.  The store has no idea because the water looks good.  They said maybe internal parasites.  There are no funky scale marks, no gill issues, and no behavioral indications (prior to Monday's death).  I thought everything was going great!  Then this!  Nothing has changed. 
 
The strangest part is I live in Portland, OR and our tap water has a low pH.  For some reason, my pH has been on the higher side since the very beginning.  The substrate is gravel.  I have no shells.  The rock is that standard aquarium rock.  I added wood to lower the pH.  The plants both look fine. 
 
Please help me before I kill more fish!  I'm about to sell the tank and give up.
 
Thanks!
 
Rachael
 

 

[N0body Of The Goat]

Which Corydoras species have you have? Very few species are suitable for a 10 US gallon (~38l tank) and even fewer for 80F (~27C).
 
A 2 US gallon (~20%) weekly water change is considered quite low for many keepers, I do at least 50% weekly changes on my tanks, partly because my tap water comes with ~40ppm nitrate out of the tap before the fish and bacteria turn the food into more nitrate.
 
How long have you had fish/frogs in the tank?
How did you "cycle" the tank?

 

[JohnofBothwell]

I cannot think of anything common to froga and corydoras except the water. So I would exclude parasites or disease. The temperature is high for most corydoras. dropping to ~75oF might help. Both would go to the surface for air, so is there an oily scum at the surface which might interfere? What about air polutants. Have you painted in the house, or possibly insecticide aerosol? Does you water company add chlorine/chloramine/flouride to the water. A treatment to get rid prior to water change,?

 

[eaglesaquarium]

pH: ~7.6
ammonia: 0
nitrite: 0
nitrate: <20
kH: ???
gH: ???
tank temp: 80deg F

Chemical Additives or Media in your tank: pH salt to bring down (1 tiny pinch 2 weeks ago)

Tank inhabitants: Had 3 frogs, but they have died.  3 cories, but 2 have died.  Only 1 cory in the tank.
 

 
I didn't catch if you mentioned which species you have, but 80 degrees is rather high for many cories.  Few can tolerate that level of temperature for prolonged periods.  Another issue I saw was the mention of an addition of salt.  Cories are extremely sensitive to salt.  
 
 
When you say "pH salt", do you mean like a 'water softener'?  
 
How did you add this 'salt' to the tank?  Was it just a pinch of salt added directly into the tank, or was it dissolved in water first?

 

[RJLB119]

They are salt and pepper cories.
The heater only has a single temperature.
The powder was a pH neutralizer.
Portland water has chlorine and I do add dechlorinator to the new water before putting it in the tank.
There has been no painting or spraying or anything new in the house. Perhaps I had soap on my hands one day when i reached in to grab a piece of plant. I cannot understand why there was this sudden change. They were happy for a little over a month.

 

[eaglesaquarium]

I'm not sure, but I think the issue was/is the pH neutralizer.  I'm not a proponent of using those types of products, as generally speaking they cause more harm than they solve.  They drop or raise pH rapidly and they "wear off" and the pH goes back to where it was, and you end up with a yo-yo effect - which is more harmful to the fish than merely holding the pH at a constant level, even if its higher than preferred.
 
 
Regarding the heater, what heater is it?  I've never heard of a heater without an adjustment option.  What many watts is it?

 

[RJLB119]

At this point, should I do anything? The tank is now fishless. Complete water change? Get new gravel?

When do I know the tank is ready for new fish? I don't know the heater name. I plugged it in and it was working. The temp is constant. The plants are great. Maybe there is something in the water I can't see or test for. I'm really just looking for a happy and healthy aquarium experience. Maybe it's like having a black thumb for gardening - some of us aren't suposed to do it.

 

[eaglesaquarium]

Not to worry, a ten gallon tank can be a bit trickier than a larger volume tank at times.
 
 
Here's what I'd do:  
 
1 - 100% water change
2 - Let the tank run for about a day or two, empty. 
3 - Another 100% water change - this should clear sufficient of the pH adjuster stuff that this won't be an issue for the future.
4 - Let the tank run for another day and test it.  Test it for pH and nitrate.  This should match your tap water pretty closely.
 
5 - Your bacteria will still be viable, so no worries there.  Buy fish that match the pH and the temp.  Your pH and temp don't really match well with the corys you were keeping.  Salt and Pepper's prefer pH that's between 6.2-7.2.  Temps are best 72-79F.
 
So, you need to find fish that work at 80F, pH around 7.6 and fit well in a 10 gallon.
 
 
A small shoaling species like Lambchop rasboras would work in that tank - a group of 8-12 would be fine in that tank - and fully stock you.  I'd start with about 5, and then bump it to 8 about 2-4 weeks later.  Then up to 12 another 2-4 weeks later.   They are small enough to work with the tank.  They can handle pH in that range, although its on the high side for them, and they can handle the temp as well.  

 

[RJLB119]

Ok. Thanks for those tips. I think I'll look into a different heater and figure out my high pH. I liked the cory fish. We'll see. Thanks again.

 

[eaglesaquarium]

Corys are my favorites, but very few are appropriate for a 10 gallon.

 

[RJLB119]

Scratch that - my last cory is still holding on.  Anything I should do to help?  Another partial water change?

 

[zupeer]

I don't really have any advice but I just went through the same thing with all of my cories... I lost all 4 of them to the same thing. One day they were fine, the next they were either dead or going limp. Water parameters were fine, no external damages.... I think what caused their death may have been the heater. Mines around 80-82F and I also have a heater that's non adjustable, so it's a one setting temperature. What's weird though is I had used an Ich treatment (Kordon Plus) and they started dying not shortly after that. My conclusion is either the higher temp. waters killed them or they had long term affects from the medicine. 
Wish I had some tips for ya but I understand what you just went through. It's extremely stressful to not know the true cause. Hope you have more luck next time

 

[RJLB119]

I don't really have any advice but I just went through the same thing with all of my cories... I lost all 4 of them to the same thing. One day they were fine, the next they were either dead or going limp. Water parameters were fine, no external damages.... I think what caused their death may have been the heater. Mines around 80-82F and I also have a heater that's non adjustable, so it's a one setting temperature. What's weird though is I had used an Ich treatment (Kordon Plus) and they started dying not shortly after that. My conclusion is either the higher temp. waters killed them or they had long term affects from the medicine. 
Wish I had some tips for ya but I understand what you just went through. It's extremely stressful to not know the true cause. Hope you have more luck next time

 
I feel bad saying I'm happy to hear somebody else has had a similar problem, but it is nice to know I'm not the only one experiencing unknown fish death.  Maybe those heaters are no good.
 
My biggest problem is figuring out why the pH is so high.  My tap water is about 6.8-7.2, but my aquarium is reading up near 7.8.

 

[eaglesaquarium]

What is the tap water reading when leaving it to sit out for 24 hours?

I don't really have any advice but I just went through the same thing with all of my cories... I lost all 4 of them to the same thing. One day they were fine, the next they were either dead or going limp. Water parameters were fine, no external damages.... I think what caused their death may have been the heater. Mines around 80-82F and I also have a heater that's non adjustable, so it's a one setting temperature. What's weird though is I had used an Ich treatment (Kordon Plus) and they started dying not shortly after that. My conclusion is either the higher temp. waters killed them or they had long term affects from the medicine. 
Wish I had some tips for ya but I understand what you just went through. It's extremely stressful to not know the true cause. Hope you have more luck next time

 
 
Corydoras are notoriously sensitive to meds (as many scaleless fish are).  Generally the recommendation is to go with a half-dose for twice as long with corys in the tank for ich.
 
Also the species of corydoras matters in regards to the temps.  Sterbai can handle higher temps, but other species really can't.

 

[RJLB119]

I'll run some tests and get back to you on that...