Re: How much of a problem is this exposure of EDTA to my frogs?
Many things are essential in "trace" amounts, but toxic [even highly so] at higher levels. Copper is one of those things which is well-established as toxic to amphibians [in other than background/trace levels].
For a wealth of references, google the following:
amphibia toxicity copper pdf
Those four words together, no quotes as the four terms are vital but aren't likely to form a phrase. "pdf" is added because most academic papers will be in pdf format. "Amphibia" is used in lieu of "amphibian" because the former is the term which will be used in ALL relevant papers, while the latter may or may not be. Substitute whatever other words you wish for comparable searches
The trend is to post names and numbers of "pets" here. That seems...um...bulky.
23+ species of salamander
28+ families and subfamilies of reptile, amphibian, and arachnid.
Only one has a name. The Beast.