Active ingredients in Furan-2: 60 mg Nitrofurazone and 25 mg Furazolidone per packet (each packet treats 10 g).
note this is older information so API may've adjusted the amounts
Note that both components are photo-sensitive so keep things dim (not sure if this is on the packet or not)
BUT (& this is why I used to rail at the aquarium product industry)
Furazolidone
20mg/litre continuous bath for 5 days
Nitrofurazone (brand name Furanace in older literature) - external infections only as there appears to be no actual uptake, dips are recommended protocol on this med rather than continuous baths
189–756 mg/10 gallons for1 h, repeat daily for 10 days
378 mg/10 gallons for 6-12 h, repeat daily for 10 days
There is often synergy of drugs but I couldn't find anything scientific regarding API's mix
(as I recall most fish infections are gram -ve (don't quote me on this as there may be new evidence of more gram +ve infectiions), then there are the ones such as Mycobacterium marinum (fish TB) which don't take up gram stain so not classified by that term)
This article is well worth perusing
Bacterial & Parasitic Diseases of Pet Fish
it's a decent "broad stroke" article that is very generously shared by the author for personal use (2009)
Chris Andrews et al
The Manual of Fish Health is slightly dated but the photos & basic information are still valid
( "new" diseases have since been identified, some old ones have updated information, (acquired)antibiotic resistance is a significant factor ... eg Nitrofurazone resistance has been reported in various bacteria)
I do know people that are great fans of Furan-2
I've just never been convinced myself, I used it back when (most fish display significant stress - which is always a major consideration in fish as it suppresses the immune system) & switched to Kannamcyn & other Seachem products (the medications they market have scientific basis in ornamental fish studies & are often pure compounds without addiitives ... even their "Focus" has proven activity)
Most manufacturers are very conservative in their dosing protocols, so while it's always good to begin with a half dose, observe fish for 30-60min, then add the remaining dose - it's also common for hobbyist medications to be delivered at below "threshold" concentration for active ingredient levels.
I suggest that you remove the choco's to a quarantine tank of manageable volume eg, 10 -20 gal so that you can easily perform daily water changes & afford to medicate daily.
Again despite packet directions, most studies done with medicating fish are based upon daily water change & daily application of active ingredient protocols - most meds degrade under aquarium conditions so this way active ingredient levels are more consistent.
In general the toxicity vs treatment dosage is quite large (often factors of 10x or more - though there are always "sensitive" species)
If possible set up 2 x10 gal tanks,
Day 1, Tank 1 - dose & add fish
Day 2, Tank 2 - dose & transfer fish
Day 3, Tank1 has been emptied & wiped down & refilled with suitable water - dose & transfer fish
etc
Note that I do not find choco's sensitive to water changes, I balance temp etc & they always seem "happier" even when I accidentally do 90% rather than the intended 60 - 70%
(again I began with conservative water changes as is generally recommended with these fish: note that my tap is rainwater soft)
Dim lighting, sponge filter is all you need, if humid, tanks can be uncovered (re labyrinth fish), though I prefer to keep covered re jumping
Temperature - if anything bacterial, stay on the low side (23-25C for S osphromenoides)
If parasitic, elevated temp is generally recommended as higher temp means more active metabolism in fish which can help EXCEPT if loads of gill involvement the lowered oxygen levels in water can be more detrimental than the metabolic boost.
Apologies on the lecture
)
(except the Neocaridinae shrimp said different) ... they got more bloodworm for dinner 