As per the above I posted, yes, prevention is the best method of avoiding fish diseases but once you've spun the ball in the wrong direction, more drastic measures are required to fix the situation.The same study points out that all cases were triggered by prior issue with water quality...but resuming water quality, although alleviating the problem, would not cure the disease outbreak...As usual prevention is the best cure..
From the studies I've read recently, it is always a mixture of pathogens involved and never just one. A parasite is always the major player accompanied by either bacteria, fungus or/and other parasites/worms. Bacteria is almost always secondary. When the fish's immune system is weakened, it seems it just gets attacked big time by what would not normally affect a healthy fish.
In this study below on discus, the pathogens involved were bacteria: A Hydrophila, fungus: Fusarium sp. and at 80% flagellates: Spironucleus Vortens.
Note the clinical signs:
Naturally infected Symphysodon spp showed ulceration on the skin especiallyon the head and dorsal fins. Fish suffered from exophthalmia, eye cloudiness,congested gills abdominal distention,excessive body mucus, frayed dorsal fin and tail rot
They divided the fish in 6 groups. The group treated with metro at 5ppm with 50% daily water changes for 3 days, fully recovered post treatment.
The other group of fish that made full recovery was those in which the tank was maintained at 30C temperature, no chemical treatment involved....
In both groups spironeucleus was not detected 2 weeks post treatment.
The fish in the control groups all died.
https://www.academia.edu/8813717/Ca...cus_fish_Symphysodon_and_trials_for_treatment
Apart from the above mentioned, from other studies I've come across on spironucleus vortens:
Metronidazole at 6.6 mg/litre for 5 days
Temperature maintained at 31C for 4 days
Magnesium sulfate in feed as per RD. extensive thread on the matter and scientific studies.
Anecdotal in discus treatment, 500 mg metronidazole per 10G of water for 10 days. (double the study recommended dose)
Anecdotal in discus treatment, 33-36C maintained for 4-5 days. (obviously way higher temps recommended than the studies...)
I think that some parasites can be eradicated while still not blown full force and if I bought a cichlid, my first action would be prevention in the form of treatment. Looking at these studies, cranking the temperature up is enough...providing you have fish that can handle it...
Although in studies it is mentioned that parasites are naturally occurring in nature, the presence of these parasites in the fish in aquarium conditions can cause an outbreak and death, or at least chronic issues, interfere with growth and nutrition, etc..
Personally I think that it may be no harm to apply a preventative treatment for flagellates, specifically in cichlids, along with subsequent de-worming for nematodes and cestodes, providing that according to literature one can actually completely eliminate these in the early stages. In small amounts the fish may not show clinical signs, providing good water conditions, but it's a bomb waiting to explode..