I would not use it in your main tank. Despite what they say an antibiotic will disrupt both good and bad bacteria.
Here's an excerpt from a faq where Anthony Calfo answers questions on using Maracyn in display tank:
Maracyn Plus safe for display? Ahhh...no.
The guy at my LFS insists that Maracyn Plus (encapsulated Sulfadimidine + Trimethoprim) is safe for display tanks with live rock and inverts.
<hehhehehehhehhe...hahhahahhahhah... wooooooo hoo! Ahhh... no.>
I am not convinced.
<healthy and accurate skepticism>
What do you think?
<unquestionably not safe to many desirable life forms. You do know/recall the root/def of the word anti-biotics? "against-life". This medicine WILL harm and kill desirable and undesirable microscopic organisms and facultiers (like your living filter/live rock)>
I've got a Sailfin with a cloudy white area on caudal fin that may be a fungus infection. Symptoms so far do not shout ich or velvet. Thanks, George.
<most all sick livestock are best removed to a proper QT tank for these and other reasons. Anthony>
Anti-biotic administration
Anthony, going to move from Metronidazole to an anti-biotic like Maracyn
<gram-positive drug, rarely effective as such spectrum infections are less common, and is extremely damaging to good bacterial fauna in tank>
or Maracyn II
<synthetic tetracycline, broad-spectrum... better choice than the Erythromycin choice above...still a poor choice>
and see if I can cure some of this fin spots. Anyhow, most of
the anti-biotics are say dissolve a tablet in 10/20 gallons of water. They also say they are good bacteria safe (though it doesn't make sense).
<exactly...bull.>
Anyhow, I'm wondering if I can crush and administer via food (like soaking brine in it or something) rather than water dissolution ? Your thoughts ?
<not recommended without a tried and true prescription. If you feel that you must medicate with anti-biotics, best bet is in a bare-bottomed QT tank with a Furazolidone-Nitrofurazone combination>
regards,
Ed
<Anthony>