Daydrakon, Ferrdrakon (K) and KramerDrak contain copper. This is very toxic for invertebrates.
Can Daydrakon, Ferrdrakon (K) and KramerDrak be used in pools with invertebrates?

Copper is the emotive term which causes alarm among all invertebrate owners!

Daydrakon, Ferrdrakon (K) and KramerDrak contain a lot of other toxic heavy metals

including iron, manganese, nickel, cobalt, zinc and molybdenum.

Seriously, copper is a trace element which is just as essential for invertebrates as it is for other animals (not to mention for plants). In this case, the dose determines where it is beneficial and necessary or excessive and damaging (the same applies to the other metals listed). The values achievable via fertilisation with Daydrakon, Ferrdrakon (K) and KramerDrak are 1,000 times below toxic concentrations. In addition, they are all used as chelatic forms, the toxicity of which is normally 100 times lower than that of the free Ions.
So theoretically, the absolute all-clear can be given.

Practical experience: I keep shrimps, crabs and snails in fertilised pools with plants, others who use Daydrakon, Ferrdrakon (K) and KramerDrak also do this without any irregularities becoming apparent.