Formalin bath questions

[Big E]

Can a get a standard procedure that most people run for a Formalin bath? Dose levels, duration, ect.

I have a bottle of Formalin that I bought about 1.5 years ago and has never been opened. Is it still good? I've read a few things about it going bad over time and killing fish?

 

[mattcoug]

Keep it simple: use as a DIP(not bath, means something else) - 1ml per gallon for up to 50 min. Remove fish early if they are stressed. Always have very vigorous aeration!! Depending on what you are doing it for, will indicate how often, and how many times, to repeat. Always put fish into clean, disinfected tank/water after dip, not back into same tank. Never dip a fish with a open wound. Some fish are very sensitive and can only tolerate a few minutes.

If it is Formalin MS by FishVet it should be ok because (1) it is airtight packaging so formalin remains inside, and (2) it is stabilized with alcohol. If your bottle doesn't meet these, then it could be bad because (1) formalin will evaporate, leaving water and (2) formalin will form a white precipitate that will kill your fish. So if there is a white precipitate - throw it out. But in general for any med, if in doubt, throw it out.

 

[Big E]

Thanks for the response..............I meant dip, mainly looking for mix amounts and time duration. I believe I was doing 30 min. back when I did them years ago.

There is no precipitate in the bottle.......the brand is APpro.

This is more for preventative........before they go into QT.

 

[mitchrapp]

Just make sure to find out the formaldehyde percentage. The 1ml/gal recommendation is based on 37% formaldehyde, which yields around 250 ppm.

 

[ThRoewer]

Just make sure to find out the formaldehyde percentage. The 1ml/gal recommendation is based on 37% formaldehyde, which yields around 250 ppm.

It is way less than 250 ppm, more in the range of 100 ppm.
I would consider the safe range to be below 150 ppm.
In my experience 250 ppm will burn the fish's skin and may do more damage than good. If you go that high the bath should be much shorter.

I would always go with Formalin MS and follow their dosage of 20 drops per gallon (5.3 drops per liter) for a 45 to 50 minute bath. I've treated some fragile fish with that and none ever showed any signs, even if I added a drop per quart more

 

[tassod]

What would be an ideal setup to DIP a new fish in formalin prior to putting in a QT? Would a 5g bucket with an air stone and heater be fine? Or perhaps a small 5g tank with a small PH and heater?

 

[mitchrapp]

It is way less than 250 ppm, more in the range of 100 ppm.
I would consider the safe range to be below 150 ppm.
In my experience 250 ppm will burn the fish's skin and may do more damage than good. If you go that high the bath should be much shorter.

I would always go with Formalin MS and follow their dosage of 20 drops per gallon (5.3 drops per liter) for a 45 to 50 minute bath. I've treated some fragile fish with that and none ever showed any signs, even if I added a drop per quart more

The dosage is very confusing as different sources say different things with different units, etc. However, this article equates 1 ml/gal of formalin (37% formaldehyde) with 250 ppm:

http://fisheries.tamu.edu/files/2013/09/Use-of-Formalin-to-Control-Fish-Parasites.pdf

"For short-term baths a concentration of 250 mg/l, or 1 ml per gallon, can be delivered for 30 to 60 minutes."

As does Edward Noga in his 2011 Fish Disease Diagnosis and Treatment book:

https://books.google.com/books?id=M...l#v=onepage&q=formalin dosage 250 ppm&f=false

"...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...."

However it also says "When temperatures are high (>21 C [=70 F] for warm water fish...do not use >167 ppm (=0.167 ml/l= 184 mg/l = 0.63 ml/gallon) (Warren 1981; Jensen and Durborow 1984)...." The University of Florida article also mentions not using more than 150 ppm for temps greater than 70 F. This would mean that 1 ml/gal at temps greater than 70F would be overdosing. But I've done dips above 70F (but below 80F) at 1ml/gal and the fish have done fine.

 

[mitchrapp]

What would be an ideal setup to DIP a new fish in formalin prior to putting in a QT? Would a 5g bucket with an air stone and heater be fine? Or perhaps a small 5g tank with a small PH and heater?

I've done it in a 5g bucket and airstone just fine. On my last fish, I didn't do it immediately. I do TTM on all fish, so I waited for the 2nd transfer to do it. I took like 3 gallons of the qt water that he was in and put it in a 5 gal container with a heater set to 78 F and an airstone. I added the formalin and let it aerate for 1-2 hours. Then I took out the heater (I didn't want to risk going above 80 F) and dipped the fish for 45 min. Then I dipped the fish in another bucket of clean SW for a few minutes to rinse him, then transferred him into the new QT.

 

[tassod]

I've done it in a 5g bucket and airstone just fine. On my last fish, I didn't do it immediately. I do TTM on all fish, so I waited for the 2nd transfer to do it. I took like 3 gallons of the qt water that he was in and put it in a 5 gal container with a heater set to 78 F and an airstone. I added the formalin and let it aerate for 1-2 hours. Then I took out the heater (I didn't want to risk going above 80 F) and dipped the fish for 45 min. Then I dipped the fish in another bucket of clean SW for a few minutes to rinse him, then transferred him into the new QT.

Thanks for the info

 

[ThRoewer]

I have no big fish so I do it in a 1/2 gallon plastic tank (pet carrier from petco) that I fill with about a quart. As a pump I use a small Jebao fountain pump.
Clear plastic has the advantage that I can closely monitor the fish during the bath.

The dosage is very confusing as different sources say different things with different units, etc. However, this article equates 1 ml/gal of formalin (37% formaldehyde) with 250 ppm:

http://fisheries.tamu.edu/files/2013/09/Use-of-Formalin-to-Control-Fish-Parasites.pdf

"For short-term baths a concentration of 250 mg/l, or 1 ml per gallon, can be delivered for 30 to 60 minutes."

As does Edward Noga in his 2011 Fish Disease Diagnosis and Treatment book:

https://books.google.com/books?id=M...l#v=onepage&q=formalin dosage 250 ppm&f=false

"...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...."

1 ml per liter is 1000 ppm - but this doesn't account for the actual concentration of the formalin solution
1 ml formalin 37% only contains 0.37 ml of pure formalin which would bring the above down to 370 ppm
1 ml formalin 37% per 3.78 liter (=1 US gal) would give 98 ppm of actual formalin in the solution.

So Noga is either wrong or too unspecific. Keep in mind that Noga's book is a compilation of many 3rd party works and not original research. Some details may have fallen through the cracks or were misinterpreted.
I'm also wondering if the actual works have been consulted or just the abstracts. The latter case would be dangerous as abstracts are often vague and sometimes outright misleading if you don't know the details of that particular work.

However it also says "When temperatures are high (>21 C [=70 F] for warm water fish...do not use >167 ppm (=0.167 ml/l= 184 mg/l = 0.63 ml/gallon) (Warren 1981; Jensen and Durborow 1984)...." The University of Florida article also mentions not using more than 150 ppm for temps greater than 70 F. This would mean that 1 ml/gal at temps greater than 70F would be overdosing. But I've done dips above 70F (but below 80F) at 1ml/gal and the fish have done fine.

This is another issue. Much of the research is done with food fish in mind which predominantly are cooler water fish.

As for the 1 ml formalin 37% per gallon (US): that's not even 100 ppm as I have shown above.

 

[mitchrapp]

Here's another reference, Fish Diseases and Disorders, edited by P. T. K. Woo, University of Guelph, Canada:

https://books.google.com/books?id=b...Ch13-QZX#v=onepage&q=250 ppm formalin&f=false

"Fishes in aquaria are treated with 25 ppm (1 ml formalin to 10 gallons of H2O) of formalin on alternate days until the infection is cleared...."

So 1 ml formalin per gallon = 250 ppm formalin.

We are talking about ppm of formalin (37% formaldehyde) not ppm of formaldehyde. Maybe that's where the confusion lies. From Noga:

"Formalin is an aqueous solution of 37-40% formaldehyde gas (which equals 100% formalin)...."

This is important because if one assumes 1 ml/gal of formalin is only 100 ppm formalin and they see the stickies and recommendations to dip at 250 ppm formalin to treat brook, and they double the dosage to 2-2.5 ml/gal, they are in trouble.

 

[ThRoewer]

"When dissolved in water, formaldehyde also forms a hydrate, methanediol, with the formula H₂C(OH)₂. This compound also exists in equilibrium with various oligomers (short polymers), depending on the concentration and temperature. A saturated water solution, of about 40% formaldehyde by volume or 37% by mass, is called "100% formalin". A small amount of stabilizer, such as methanol, is usually added to suppress oxidation and polymerization." (Wikipedia)

All these articles seem to assume a saturated solution of 37% without actually specifying it.

Still, even then 1 ml per US gallon is not 250 ppm but rather 265 ppm
250 ppm would be 1 ml per 4 liter.

 

[mattcoug]

I believe most of the confusion is the difference between formaldehyde and formalin. As earlier mentioned, formalin is water that is saturated with formaldehyde. This saturated water is about 37% formaldehyde and 63% h20.

So 100ppm of formaldehyde is roughly 250ppm of formalin.

Of course all these number are highly rounded- and this also adds to the confusion.

 

[mattcoug]

I would always go with Formalin MS and follow their dosage of 20 drops per gallon

For OP - 20 drops is a rough way to get ~1ml. So this is the same advice - just different units