So, to the two questions that I have:
1. I noticed that with some of these puffers, they have two little horns sticking out on the top of their heads. Some of them are either much much more prominent than others, or the other ones don't have them at all. I was wondering why this was, because mine's seems to be really prominent. I was comparing him to the other fish when there were others in the tank with him and most of them weren't as big as his. Example:

Not my fish, but I didn't know what those little horns were called.
2. Should I mix the marine salt in with the filter, or is this a bad idea? How gradually should I put the salt water in before putting in the preferred amount?
Thank you for helping, he is kind of sick, yet happy. Bright green with nice looking gills and swimming around fast.


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