Help! African Dwarf tadpole!

[Producer]

I inherited a pair of African dwarf frogs four or five years ago and gave them a much bigger home. They live happily in my office and I have to admit I'm not a high maintenance owner. By that I mean I don't religiously clean their tank (once a month) or use anything other than spring water when I change (never done a pH test or anything.) I feed them every 3-4 days crushed freeze dried blood worms (top) and newt food (bottom) and they eat both.

I hear them singing occasionally and see them locked up doing their business. Then all of a sudden last Saturday I glance up and notice a single tiny tadpole! Since then he's doubled in size. He at first stayed only on top but now he's wandering more comfortably. Now what to do??? I've read in places that it's kind of rare??

Two obvious questions: what do I feed this little guy? I crushed dried bloodworms to a powder and he seems to eat it (or at least nudge at it.) If it ain't broke don't fix it and move on??

Lastly, the tank does need cleaning (i guess that's dead eggs and sheddings) but now I'm scared that what would be a 'usual water change' for parents might be catastrophic for the little guy.

Any help is appreciated... the more the better. Tried to attach photos here too.