Nursery tank for guppy fry?

Bigger the better as you are going to have to rear the fry to be big enough not to be eaten by the catfish, so they need to be bigger than if you just had adult guppies.

Maybe a 20 gal? Make it a decent size because you might need to house 50 x 1/2"

guppies in there. The tank is then also useful for keeping or breeding other fish species in the future

An uncycled tank is going to be a problem, but you can jump start the cycle from your existing tank by moving gravel, fitler media or even just squeezing a dirty filter into the new tank. Doing that and having a larger than minimum tank will give you a better chance. The old tank water is not what you need, you need solid materials like filter sponges or gravel.

Ian

You need a 5 gal tank for the fry for about 3 weeks, then a 10 gal .. That's if your femal guppies

have 10 to 20 fry each.. But they could have 30 or more fry, each - and then you'll need that 10 within a day or two.

You must use cycled water, you can use 75% of the water from your established tank, and 25% fresh..