right didn't understand your setup
worms do many different things to the organics/microbes they ingest since you have composting worms Basil1 you probably are aware of at least some of what they do. with the fear of being banned from this site; i believe they provide more to the ponics systems then the fish do, but not a whole lot of people are into using earthworms for their meat source and this is what aquaponics is about a total efficient compact self contained system. if composting worms can be incorporated i believe it broadens the selection of quality food crops that can be produced. however, even without the worms with an addition of at least CA and Mg you will note a much better growing environment for your plants either ornamental or food.
I use to use epsom salts to bring tropical fish out of shock and crushed coral or oyster shells have been incorporated in both freshwater and saltwater systems for 30yrs that i know of for wet dry systems if nothing else then to provide CA for the microbes
Don't know what kind of eel you have tire track or fire eel?

Rich