African dwarf frogs

[Treebeard]

My dw set up a 10 gallon tank with a betta and African dwarf frogsbgut she is having a horrible time keeping the frogs alive. The tank was properly cycled and parameters all good. She feeds the frogs and the betta blood worms from a feeding dish and they all seemed to be eating well, but eventually, one by one they die.
She also uses RO/DI water.

She read somewhere that metal can cause problems for ADFs so she removed two screws that were securing a piece of wood to a rock. She also read that frogs need the basic minerals contained in water, but thinks that the RO/DI water may no longer contain these minerals.

These frogs are supposed to be easy to keep and needless to say she is becoming very frustrated. Any advice on how to keep these guys, and what she may be doing wrong would be greatly appreciated!