mine are in a 55 gallon community tank,water temp about 75 degrees,neutral to slightly hard water no plants juts a couple of rocks and a piece of driftwood...no sand got gravel....penguin filters and power head so good current

I think a critical tank condition is having a combination of Male and Female Cory's!

I had Cory's and Bristlenose for 12 years before any breeding took place. And I'm certain it's because I was unlucky to pick up any pairs at the outlets. Probaly my own fault for always picking the young ones.

And there's always the Seasonal Rain thing. Mine can almost be guaranteed to lay after a cold water change. Even more so if you've left it a couple of weeks.