20 Gallon Tank Corydoras Food Crisis

Hey all,

I have a situation regarding Corydoras (in my case Juli Cories).
I started out with 6 of the little guys as babies, went through 3 months quarantine with no issues.
They grew fine in quarantine, and then I moved them to a sand-based 20 gallon long tank.

A month or so ago I replaced the sand with eco-complete black gravel for my new java fern, and other plants. I bleached my plants and soaked with Prime before placing them into the tanks.

The corydoras do share the 20 gallon long tank with an adult rainbow shark, but he tends to keep to himself unless the cories go in his log house.
The cories often ignore the shark during feeding time, so they forage around plenty, I have watched from a distance. And yes, I know Mr. Shark would like a bigger tank but I don't have any room left and he was a rescue, so I did the best I could.

Tank Stats:
Nitrates: 15ppm before weekly water change yesterday.
Ammonia: 0ppm
Nitrites: 0ppm
Temp: 80F

Since adding the new substrate, I have noticed my cordoras getting thinner and dying off. I have lost 2 so far. I feed these guys generously everyday so I am perplexed why I am losing them.
The female corys seem to be thriving while my smaller males are dropping. They have their barbels almost gone vs the females with long healthy looking ones.
The Hikari micro-pellets, NLS regular pellets, algae wafers, and flakes I feed them are on top of the substrate, so I don't understand why it seems they are starving to death.
I have noticed the cories with the worn down barbels completely missing food that they literally touch with their stubby barbels.
I have been feeding some bronze cories in another tank with the same diet with no issues for a few years now.
Is there a problem with the male Julii corydoras as a species?

 

Internal parasites, maybe? Least thats what first springs to mind.

 

Hmm, I have some prazipro on me, so I guess I can try that. Thank you for the suggestion.

 

I don't know what the exact reason is but I have noticed that Eco Complete often causes issues in case of corys.
Several "barbelloss" threads has occured with Eco Complete as substrate.

 

Interesting, I wonder what the substrate consists of. I will have to do some digging. I'll change my substrate this week and see if I get any better results.

 

I don't know what the exact reason is but I have noticed that Eco Complete often causes issues in case of corys.
Several "barbelloss" threads has occured with Eco Complete as substrate.

I kept Julis for years on eco complete. Their barbels were always long and healthy.

 

I kept Julis for years on eco complete. Their barbels were always long and healthy.

As always : There are always exceptions.
Only reflecting experiences out of several threads I have read over the years.
No scientific proof or what so ever.

 

Perhaps I got some sharper rocks than normal, but who knows. I am going to give the cories some smoother gravel.