Hi Kyle,

I´m very sorry to read this.

It´s a good thing you could return the tank (very accomodating behavior of the store). Obviously, there was something very wrong with the whole batch of frogs if you actually could see dead ones in the tank of the LSF.

I would try to get frogs from private breeders (local aquarium clubs, classified ads etc) which were raised, fed and kept adequately. Also, it´s always a good idea to get as much information as possible about the needs of new pets before buying , if you didn´t already. This is a nice article to start FrogsArtNeale

Good luck!

Edit: Somehow, I didn´t see your message before. 5.5 gal is ok for ADFs, but it should be cycled. Frogs aren´t as nitrite-sensitive as fish, but it´s still poisonous in higher amounts. 24 hours after the setup, the nitrogen cycle didn´t start yet, so it´s pretty normal that your readings were fine. Please read about the cycling process if necessary; now that you unfortunately lost your frogs, there will be enough time to let the tank cycle.
Bloodworms are ok as a treat, but I would recommend alternating with brine shrimps, daphnia, glassworms, black mosquito larvae, mysis, pieces of earthworms, tubifex, enchytraea etc. as bloodworms don´t contain all the nutrients an ADF needs. All foods should be life or frozen instead of freeze dried.