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Hello! I'm new to the forum, so hopefully I'm asking this in the correct place.

I had 4 albino cories and a betta in an established ten gallon tank. I was in the process of cleaning out a 20 gal long and replacing the gravel with sand (same type of CaribSea sand I have in the 10 gal, but all new). Once it was ready, I had planned to move all 5 fish into the 20 gal and add another 2-3 albino cories so they could be in a bigger shoal.

But in the meantime, my cories laid eggs! (first time). I left most of the eggs on the glass and they were eaten. But the few I saved and put into a mesh breeder box hatched 3 days later and now I have 12 cory fry zipping around in the net breeder and getting bigger every day.

I'm looking for advice on how and when I should go about moving cories over into the 20 gallon tank. I've already moved the betta over to the 20 gal, and it's got filter media from an established tank's filter in it. So theoretically, that's an instantly cycled tank, right? The betta is doing well, but they're less picky than cories in my experience. And the babies are extra sensitive, right?

How long would you give it before moving the 4 adult cories into the bigger tank? Or is there an advantage to having adults in with the babies once they're big enough to leave the breeder box? How long before the bioload in the 10 gallon is too great? I could put the breeder net in the 20 gallon, but that makes me nervous since it's basically a new tank, except for the filter media.

If anyone has any advice, I would love to hear it! Thanks so much!

Unless I am wrong, the betta would most likely eat cory eggs and fry. Also many corys are known for eating their own eggs. The old rule of thumb that most fish will eat whatever fits in the mouth (and on occasion can get something stuck that is too big) holds true. In most cases, the highest survival rate involves pulling the eggs to protect them until they hatch and then continuing to protect and feed them in a safe space until they are too big to get eaten by tank-mates. Then you can add them back to the main tank.

If you are planning to sell, trade or give them away, it is a lot easier to retrieve them from a growout tank than a community tank with decor and possibly live plants.

Bear in mind that a tank with enough cover in which fry can hide will generally prevent the loss of 100% of a spawn. But if your goal is to maximize survival rates, then you should pull the eggs and deal with them in a separate small hatching tank. After that I would move them to a larger dedicated growout tank. Maybe a 2.5 gal to hach the eggs to free swimming and then a 10 gal to grow them in to a size you move them out to wherever you want. If you are successful with this over time, you may need more and bigger tanks. Have a look at this thread "What's the record for consecutive days spawning in your corys?" viewtopic.php?f=6&t=45338