As an MD married to a DVM let me chime in a little about antibiotics here as i think there is a lot of anecdotal evidence out there with little understanding of the actual science. As aquarists, 99.9% of the time we are treating infections empirically - we have no clue what we are treating as few of us have the resources to send a specimen to a lab to get a correct ID. Ciprofloxacin is a broad spectrum antibiotic with good coverage of gram positive and negative bacteria. It is particularly effective against ciliated bacteria like Vibrio that are frequently cited as marine pathogens (see whole thread on treating host anemones with Cipro in the anemone forum). It binds to an enzyme unique to bacteria that essentially keeps them from using their DNA for any purpose including replication. It is bacteriocidal unlike the macrolide antibiotics (erythromycin) which are bacteriostatic (keeps them from replicating). Macrolides are also very broad spectrum and do cover some atypical species of bacteria that might not be covered by Cipro. Sulfa drugs like trimethoprim/sulfamethoxazole have a similar spectrum of coverage to the fluoroquinolones (Cipro, enrofloxacin,...) but work by poisoning bacterial synthesis of folate which they require for reproduction of their DNA.
If you do not feel the Cipro is working, I highly doubt changing to another class of antibiotics with a similar spectrum is going to make much of a difference. You might consider adding a second agent rather than switching from one to another, but it makes me nervous to be treating one fish with so many medications. If you feel the Cipro is having some effect, you might consider increasing the dose - it is possible your dose is just at/below the threshold necessary to have an effect. Observe the fish after you increase the dose so that you can get it out if it appears to be having some toxic effect- don't make the mistake of doing it before bed. The listed dose for most fish antibiotics is extrapolated from human/small animal dosing and a good measure of trial and error. Different animals eliminate/metabolize meds at different rates. I doubt, other than for food fish, that the elimination/metabolization rates for fish have been studied so the correct dose is really just an educated guess.
Metronidazole has a completely different mechanism of action and covers mostly anaerobic bacteria and some protozoa. Might get you something the other meds aren't giving you.