[Asgard]

I have D.dario's and CPDs together, no problems here.
I feed the CPDs first (dry food), then I feed live food (tubifex, grindals, daphnia, mosquito larvae). Besides that I have RCS in the tank so the dario's have shrimplets to prey on.
A somewhat larger amount of live Daphina or mosquito larvae will feed them for days.
O, and both species breed in my tank, so I guess some newborn CPDs, will be eaten too.

By Threadfins you mean (Iriatherina werneri)?, the CPDs and Dario's want it much cooler (20C-25) then the rainbows (25C-32C), something to consider.

 

[Asgard]

They are perches (bass) don't kown if that's the (non tropical version) same thing as chiclids.

more info on badis/dario
http://www.practicalfishkeeping.co.uk/pfk/pages/show_article.php?article_id=626

 

[Asgard]

Yep, throw just in the food, don 't expect them to jump on it.
If you have them with other fish, feed them live food, like bloodworms/tubifex, some of them will crawl in the bottom where other fish will leave them be. Sooner or later the worms will stick their heads out,... and become dario food.

25C, you could try, but dario's also like day/night temp. changes, I keep them in a unheated tank temp. day about 24C/night about 17C the CPD also like these temps.
I don't know if Werneri's are easily affected by whitespot Threadfin article [ (ick), a disease that usually affect fish that are kept too cold for their likings. Why not keep Peacock Gudgeons with the threadfins?

 

[Asgard]

I from the Netherlands and only know LFS's who have them. But the Peacock Gudgeons would be perfect tankmates for your Threadfins and will also take flakes so how easy is that?
So if you like them, try to find some!

 

[Asgard]

It's not the feeding habit/water layers, it's the temp. differences that the fish like what could be a problem. CPD's can handle higher temps, dario's will get ill at constant temps above 25C, threadfins will get ick if kept at lower temps.