40 Gallon Tank 2 Cory Catfish die in a day...

I woke up this morning and one pepper cory died I had 4 total. Although I bought them during 2 different trips and 2 are significantly bigger than the 2 smaller ones. The ones that died are the smaller ones. I have had them for maybe 1.5-2 months now. The smaller ones have been in my tank longer than the 2 bigger ones. The other small one is not doing well and floating on the top of the water upside down and occasionally will try to swim back down. I have previously had 2 panda cories that also died in this tank. Maybe I'm not destined to have cory catfish?!

They were not behaving erratically before this. I feed the tank pellets 2x a day and hikari sinking wafers (not algae) 2-3x a week. Everyone else seems to be acting normally. My sparkling gouramis fight each other but I have never seen them bother the corys.

I typically do a water change weekly. Last on was on Wed, ~15%. My tank is dirted, sand substrate, heavily planted.

Water test:
Nitrate: between 0-20
Nitrite: 0
Amm: 0
Hardness: hard-very hard
Chlorine: 0
Alkalinity: high
pH: alkaline (8+)

These have been stable since the tank has been set up. I have been adding Excel (NOT overdosing and only the daily one, not the additional per water change) every other day, but only once since Wed's water change. The only other changes since Wed is I lowered the flow from my canister filter slightly (but enough to agitate water), and I added more plants on Thursday. Any suggestions welcome...

 

Did you purchase all of them from the same store? Could be bad genes. The other cory floating and having trouble swimming leads me to believe it's a swim bladder issue, which is a result of either parasites or overfeeding. How much do you feed whenever you feed? Also, why don't you use algae wafers instead?

 

Using Excel is like having ammonia in your tank. It might not be the cause of the problems but it's toxic and probably should be dealt with before looking at other causes.

 

Did you purchase all of them from the same store? Could be bad genes. The other cory floating and having trouble swimming leads me to believe it's a swim bladder issue, which is a result of either parasites or overfeeding. How much do you feed whenever you feed? Also, why don't you use algae wafers instead?

Yep, all the fish from the same store (diff visits). The 2 small ones + previous panda cories are from the same batch so that's a good theory. Would you suggest that I need to get more corys for the 2 left in my tank so they aren't lonely?

Hmm, I don't feed that much typically and the pellets the corys probably don't even get much since I have sparkling gouramis and rasboras. The pellets are gone for sure under 30 seconds lol.

I thought corys don't primarily eat algae. The Hikari sinking wafers look specifically marketed for cory catfish so I got those.

Using Excel is like having ammonia in your tank. It might not be the cause of the problems but it's toxic and probably should be dealt with before looking at other causes.

Can you elaborate why it is like ammonia? I will stop dosing for now. Thanks

 

Yep, all the fish from the same store (diff visits). The 2 small ones + previous panda cories are from the same batch so that's a good theory. Would you suggest that I need to get more corys for the 2 left in my tank so they aren't lonely?

Hmm, I don't feed that much typically and the pellets the corys probably don't even get much since I have sparkling gouramis and rasboras. The pellets are gone for sure under 30 seconds lol.

I thought corys don't primarily eat algae. The Hikari sinking wafers look specifically marketed for cory catfish so I got those.



Can you elaborate why it is like ammonia? I will stop dosing for now. Thanks

I have no experience with using Excel, so I'd focus on what the expert said first. I have 11 Corys, and I been feeding them algae wafers based on advice given by my LFS. After some quick research, you seem to be right so I'll probably add sinking pellets to their diet as well . As for getting more of them, I'd definitely recommend getting at least 2 more of the same breed, but try getting them from a different source in-case they are from a bad breeder. I know Cory breeders do a TON of inbreeding, and that can cause some really bad batches.

 

I have no experience with using Excel, so I'd focus on what the expert said first. I have 11 Corys, and I been feeding them algae wafers based on advice given by my LFS. After some quick research, you seem to be right so I'll probably add sinking pellets to their diet as well . As for getting more of them, I'd definitely recommend getting at least 2 more of the same breed, but try getting them from a different source in-case they are from a bad breeder. I know Cory breeders do a TON of inbreeding, and that can cause some really bad batches.

Thanks! In your experience does size matter? lol because I noticed the 2 smaller ones didn't hang out a lot with the 2 bigger ones even though they are the same type... the bigger ones are easily 2x the small ones haha

Another theory I have is that I killed them with the toxic bubbles while moving around plants but I don't know why the other fish are fine.

 

Thanks! In your experience does size matter? lol because I noticed the 2 smaller ones didn't hang out a lot with the 2 bigger ones even though they are the same type... the bigger ones are easily 2x the small ones haha

Another theory I have is that I killed them with the toxic bubbles while moving around plants but I don't know why the other fish are fine.

Size isn’t a huge factor, make sure they’re not small enough that they could get picked on (if you have a aggressive fish in your tank. The other corys won’t pick on it) and just look for healthy active fish.