Hey, you could try tetra parasite guard after if the api general cure doesn't work as the parasite guard has Praziquantel, Dflubenzuron, Metronidazole and Acriflavin. Whereas the General cure only has Praziquantel and Metronidazole. So maybe? I mean if you can afford to its worth a try.
In regards to the dosing. Tetra parsite guard says to treat once, waiting 48 hours and treat again. BUT if you have a real stubborn parasite it says to treat again and wait 48 hours. So that's three treatments (6 days). THEN it says to treat once a week for 3 weeks to make sure all the larvae is killed. So considering the general cure has the same ingredients bar two less then it wouldn't not hurt to do the same?
One thing I thought about is maybe the fish has hexamita also? That is a common cichlid parasitic protozoan that lives in the digestive tract and causes them not to eat from the irritation when swollowing. Maybe it has this also? In which case metronidazole is the cure. HOWEVER metronidazole needs to be treated for around 14 days to rid this parasite or even longer in some cases. The reason it takes so long is because A) metronidazole is not very water soluble and B) its a antibiotic and some antibiotics need around 14 days to fully kill something sinister off. Some people think 14 days is too long. I think it's almost not long enough as this parasite once taken hold needs a long treatment of metro to get rid of. Metro is not very toxic in proper doses so don't worry about the fish suffering from the med and helps with heaps of parasitic problems.
It baffles me why these companies only say 4 to 6 days on antibiotics. It should really depend on how sick the fish is. I often treat for longer as the duration listed on the packet is never long enough. They say it because they are frightened of liver damage. I'd rather kill the parasite or bacteria and then worry about liver damage as not treating for long enough is a lose lose situation.
If your tetra parasite guard or API general cure doesn't work and you've got the money to spend. You could try seachem metroplex and treat for a long duration of time. Like for 14 days. Then if that doesn't work you could try methylene blue in a quarantine tank. ANd if that doesn't work then I'm stumped
I too have a sick fish who I refuse to give up on who has been battling for over a month now and looks almost dead so I know what you're going through. And I refuse to give up on it until it actually dies as you never know. Something just might work.
But yeah get your filter sorted. I'm guessing the furan 2 nuked it. kanaplex doesn't nuke filters so much and neither does metroplex.
IN regards to fluval's recommendations of replacing filter cartridges ignore them and use this rule of thumb. If the filter is completely falling apart then replace it, even then you don't have to. All a filter does is polish the water and house bacteria. I don't think the bacteria are too fussy about their home, even if its falling apart I doubt they care. If you do buy fluval replacements don't buy carbon mixed with floss and noodles. Keep the carbon in its own removable thing. As that does need replacing, if you decide to even use it.