"There is anecdotal evidence (but never scientifically proven) that some fish exposed to formalin don’t live past 18-24 months. In some areas, the purchase of formalin is prohibited."
Quote taken from:
https://www.reef2reef.com/threads/formalin.290925/
Based on this i would never use this stuff as an intake step, only on fish who show clear signs of uronema or brook.
Totally understand why you might not like using it. There is published evidence that it's not ideal just after transport. However, it is specifically sold for prophylactic use (Safety Stop).
Humblefish used the word anecdotal to discuss long term concerns, as I'm sure you noticed in the passage you quoted.
Another fantastic resource is the go-to fish disease veterinary textbook, Edward Noga's "Fish Disease, Diagnosis and Treatment."
Here are a few passages from that book about the use of formalin:
"Formalin is an aqueous solution of
37 – 40% formaldehyde gas (which equals 100% forma-
lin). Formalin cross - links proteins, resulting in cell death
(van Ham and Hall 1998 ). It is an effective parasiticide
for bath treatment of most ectoparasitic protozoa and monogeneans. It has moderate - to - weak antibacterial activity. It also has moderate - to - strong activity against
water molds on eggs but is not antifungal at doses that
are nontoxic to fish."
"Formalin can be irritating to the gills, and water should
be well aerated during treatment. Formalin is more toxic
in soft, acid water and at high temperatures. Even slight
differences in dosage or exposure time can have a major
effect on toxicity (Heinen et al. 1995 ). Some fi sh, especially elasmobranchs, are sensitive to formalin, so it is
best to do a bioassay before using it on an untested fish
species. Idiopathic deaths may occur within 1 – 72 hours of treatment (Warren 1981 )."
"Formalin is contraindicated if fish have been recently
stressed (e.g., transported, shipped) or if skin ulcers are
present. Used formalin solutions should be diluted to at
least 25 ppm before discarding.
Formalin is volatile and irritating. It causes cancer in
laboratory rodents and can cause contact hypersensitivity
and lung damage in humans; solutions should be tightly
sealed during storage and not allowed to contact human
skin. Formalin should only be used in well - ventilated
areas.
Formalin should be stored in the dark and above 4 ° C
(39 ° F) to inhibit paraformaldehyde formation, a highly
ichthyotoxic white precipitate (Fig. III - 6 ). Formalin
should never be used for treating fish if paraformaldehyde is present. Methanol (12 – 15%) is added to formalin
to inhibit paraformaldehyde formation. Formalin should
not be mixed with potassium permanganate.
Formalin chemically interferes with the methods used
to commonly measure ammonia and thus accurate
ammonia readings are not possible with these methods
when using formalin"
"1. Bath
a. Add 0.125 – 0.250 ml formalin/l (= 125 – 250 ppm =
0.47 – 0.95 ml formalin/gallon), and treat for up to
60 minutes. This can be repeated two to three
times once daily if needed. When temperatures are
high ( > 21 ° C [= 70 ° F] for warm water fish or
> 10 ° C [= 50 ° F] for cold water fi sh), do not use
> 167 ppm (= 0.167 ml/l = 184 mg/liter = 0.63 ml/
gallon) (Warren 1981 ; Jensen and Durborow
1984 ). The maximum dose should only be used every 3 days. Up to 167 ppm can be used on concurrent days (Post 1983 ). Formalin is usually contraindicated if the temperature is low l 27 ° C."
Honestly though, aren't we beating a dead horse (chromis)? I posted the passage above for anyone looking for treatment info in the future, but the OP's fish all died (probably of uronemia) a month ago.
Edit: sorry for the funny formatting. Can't be easily fixed.
www.reef2reef.com
humble.fish
