Unfiltered Fry Tank?

Hello!
I currently have a problem.
My two female platys gave birth over the span of a month
The first gave birth to 12 fry {At least, that's how many I saved} Which I estimate are 3 weeks of age
My second gave birth around 3 weeks later to 15 Fry {This was three days ago}
I have a small 3 Gallon tank that I have a heater for, but no filter.
I was wondering if it would be okay to change the fry tank water with water from the aquarium each day until I can purchase a filter on the weekend?
And Is it okay to mix those fry groups?

 

Is it recommended? No. However that is exactly the way you normally deal with Killifish and Betta fry.

 

I had my 10 Fry in a 1.5 gallon heated but no filter for about 2 weeks until I got my 10gallon up and running for them. They didn't grow much in there but they are all still alive and happy in their 10g now!

 

You will need to keep up on the water changes. You may also have problems with the 3 week gap, as often the most ferocious predators of new fry are slightly older young. with a 3 gallon tank, you will have to find out...
Bear in mind that when you install the filter (for a 3, a sponge filter is good) it will do very little until it has been colonized by archaea and bacteria. It may be close to useless for a couple of weeks. I would suggest you also get some fast growing floating plants - hornwort, water wisteria or guppy grass to help filter in the interim.
Good luck - it's fun to watch them grow.

 

Everything that you are saying should be fine. However, a few things;
1) I wold change the water with dechlorinatedo tap water, or the water you use for normal water changes. Ithink would be much more efficient at removing undesirable substances than taking tank water to replace it with.
2) your fry will quickly out grow your 3g tank, or else become stunted. As soon as they are large enough to be moved back to the community tank, I would do so.
3) mixing batches of fry should be fine. Just double check that the smaller fry are too big to fit in the older fry's mouths.