The only information I can find on that dechlorinator is
here but I don't know if this is out of date as the link to the product doesn't work and Tetra's current site says it is a new formula.
In the table in the link, it says Tetra Aqua Safe contains sodium hydroxymethane sulfinate, polyvinyl pyrollidones, organic hydrocolloids, organic chelating compounds.
Tetra's website says the new formula contains "bio colloids for beneficial bacteria growth which supports the creation of clear water" (the hydrocolloids?)
Sodium hydroxymethane sulfonite is the chlorine removing chemical.
Organic chelating compounds remove metals.
Polyvinylpyrrolidone is the one that 'protects gills and mucous membranes' as stated on the front of the bottle. If you want to know what this is, I suggest you google it. Wikipedia (yes, I know, not the most reliable source) describes its uses, and they don't include coating fish!
I wouldn't use this dechlorinator.