Sterbai Corys infertile eggs??

[BRLaquatics]

Hi All,

I'm looking for some insight and advice on my breeding group of 7 sterbai corydoras.
They've spawned on three separate occasions now and each time they seem to produce 98% infertile eggs.
I managed to get 2 fry from a batch of 30 eggs last month, but the two fry perished in 3 days after hatching.
They were hatched and kept in a marina hang on breeder box.

This month they've spawned again 5/6/2020, and I collected approx 60 eggs, only to have majority of them turn the infertile white colour.
This batch of eggs was kept in a 2 Litre tub beside the main aquarium with an airstone and nano heater keeping the temp at 27 degrees Celsius.
1ml of methelyne blue was added to keep fungus at bay. I also added a catapa leaf for the fry to hide under if they ever did hatch
(today is the 11/6/2020 and no eggs have hatched)

My main questions are;

Am I doing anything wrong?

Is there anything I could do better?

Do corydoras have some sort of spawning learning curve where for the first couple of tries the eggs are infertile?

Any advice or input is welcome

Regards,
Blake

[bekateen]

Hi Blake,

I've experienced that too. Some of my best spawning groups of cories have low fertilization rates. I don't know the cause... Might be pH at time of fertilization, might be health of males (some people claim certain medications can sterilize males), might be water is too hard.

Keep at it. Good luck,
Eric

[BRLaquatics]

Hi Eric
Thank you for your reply

When they spawn next I'll make sure to test the water parameters.
Maybe that will hold some clue as to the low fertilisation rates

Cheers,
Blake

[BRLaquatics]

Hi Blake,

I've experienced that too. Some of my best spawning groups of cories have low fertilization rates. I don't know the cause... Might be pH at time of fertilization, might be health of males (some people claim certain medications can sterilize males), might be water is too hard.

Keep at it. Good luck,
Eric

The Sterbai spawned again this afternoon.
After I finished collection as many eggs as I could find and placed them into the same container with 1.0ml of methylene blue
I proceeded to do a water test.
This test was done using the liquid API brand test kit (so who knows how accurate it is, API isn't know for it's accuracy)

Ammonia 0ppm
Nitrite 0ppm
Nitrate 5.0ppm
GH 4 drops, 71.6ppm
KH 2-3 drops, 35.8-53.7ppm (it was hard to read this one as the colour only changed slightly on 2 drops, but fully changed on 3 drops)
pH 7.2 - 7.6
TDS 124ppm
Temperature 26.8 degrees celcius

I hope this can shed some insight as to why the last batch had a zero percent hatch rate.

Cheers,
Blake