[Delphinus]

Fish will know better than to eat floating gobs of kalk paste, but it's probably better to avoid an amount that will make a huge cloud.

What I do is use a really small syringe (UFA is one place you can pick these up), and a large gauge needle (the term is probably "small gauge" I don't know, what I mean is a large diameter tube). And inject the kalk paste. Not just kalk, that stuff is just spicy water to them. Mix up a small amount of supersaturated solution (i.e., there is powder at the bottom of the liquid even after mixing -- ergo, "supersaturated"), and inject that stuff (the powder at the bottom). And you have to be quick, as soon as they're poked, they'll disappear into the rock and if you don't get enough in them they'll just come back.

You can try feeding them first so that they can't make themselves as small.

As far as getting the kalk paste onto neighbouring zoos, it won't be great, but as long as you don't inject the paste into them they ought to recover.