I was worrying about the same thing but I plan to lightly bleach the coral and soak it before putting it in the tank and have the water tested afterward.
Im moving the danios to the 25 and getting a few more as for the red tailed black shark i thought they only grew to 6" but i may leave the other tetras in the other tank to avoid the plant issue.
This is my first time keeping tropical fish and so far I have 2 buenos aires tetras and 2 zebra dainos in a 10 gallon hexagon tank below.
Stocking my new 25 gal tank is the trouble im having with the tetras i have now would it be possible to stock a red finned shark with them if not any other...