Cory cats not living long

[Bix22]

I have a fully established tank for 2 yrs 20 gal long.
Parameters stay at 0 nitrite 0 ammo 7.8 ph 10-20 nitrate
It seems when I introduce Cory cats they don't last long.
Most of my other fish are almost originals - close to 2 yrs old. I've had a few deaths over the years but never any disease.

I have 5 glo light tetra
3 zebra Danio
1 Kuhli
Dwarf gourami
2 mm platy

What could be the problem? Is the pH too high? 7.8 is my tap ph (well water)


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[Werebat]

A long time ago I had a rubber lipped pleco that died in my 20G shortly after I purchased it. The water had 0 ammonia when I tested. The LFS owner told me to test the bottom of the tank not the top, so I took the sample from the bottom and what do you know, there was detectable ammonia. I had an undergravel filter at the time so maybe that made a difference?

 

[F.Sam]

Have you ever vacuumed your gravel?


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[Bix22]

Yes I vaccuum it twice a month 5 gal water changes

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[Bix22]

I have a HOB filter and sponge filter w bubbler

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[F.Sam]

I would up the water changes to 50% on a weekly basis. I do a gravelvac every time I do a PWC, so every week.


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[J.Mcpeak]

Test GH.

 

[Bix22]

What is GH

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[Pseudomugil]

Gravel can hurt cory cat's barbels. Soft sand is recommended. Also, how many cories have you been getting at a time? They like to be in schools.

 

[Coursair]

Dirty Gravel is more of an issue. Sharp gravel or sand is to be avoided.

Are they showing signs of Barbel erosion before death ?

What are you feeding ?

What species of Cory ?

How many and what temp is the tank ?

Are you using strips or liquid test kit ?




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[J.Mcpeak]

What is GH

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GH - General hardness

Normally builds up over time, it's likely in your case, and it varies depending on evaporation. While 5g twice monthly may be enough to keep nitrate low, it probably isn't enough to maintain GH at tap (source) water values.

Eg, start water is 100 GH, every month it goes up by 10.
2 years later it is 340.
That's hard water from soft/slightly hard water.
(Only water evaporates not dissolved mineral content)

Even if you do 50% each day (2-3days concurrent) it will not be the same as start point.
On a 20g tank, 5g twice a week will be ok for a while, but it will still rise slowly. You will still need to do the large water change to re align things.

(3 changes at 30% plus 2 at 50% over 5 days, this will ensure current stock doesn't suffer any stress from the change, too much too soon, you will get the same issues with your current stock)

So, you add fish that are kept in softer water into harder water, you get osmotic shock, while Cory are tough it may be enough to kill, it can be the reason for death.

That's what I guess from your given information.

 

[Bix22]

Feeding sinking pellets
Julli cory cats
Last time I bought 4; 2 died rather quickly
Api liquid kit

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