Baby fish should be kept in the small tank for a few weeks so they are closer to the food. Once they have grown a bit you can move them into a bigger tank/ container. Emergency fry tanks can be anything from a 20 litre bucket to a 200 litre plastic storage container with a lid.
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To grow tropical fish fry quickly,
Keep the water warm (28C).
Feed the babies 3-5 times per day with a food they can eat. Egg yolk or liquid fry food (usually made from egg yolk) is fine for the first 2 weeks, then add newly hatched brineshrimp and microworms. As the fry grow, add crumbled up dry foods, marine meats (fish, prawn, squid) and frozen foods like daphnia and bloodworms.
Do big daily water changes to dilute nutrients, disease organisms and growth inhibiting hormones.
Make sure any new water is free of chlorine/ chloramine before it's added to the tank; and make sure it has a similar chemistry (pH, GH, KH) and temperature to the fry tank.