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Malathion - fish lice & snail pests


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Oct 26, 2009, 2:59 PM

Post #1 of 11 (7525 views)
Malathion - fish lice & snail pests Can't Post


I've posted questions before re my snail pest of wc my journey towards eradicating took me to using Malathion (57% EC).

My initial introduction to this pesticide was during my bout with fish lice- argulus. I used Masoten powder to dose them initially but turned to Malathion after reading the label that Masoten was an Organophosphate, similar to Malathion. My research took me to various websites advocating its use, even in this forum in a post by 'regallion' back in 2004, citing an article from www.bonniesplants.com. I presume regallion used it in his pond at the recommended dose of 2cc/1,000 gallons successfully.

As the rejoinder to that post was that "even minute quantities of this organophosphate can kill fish", I took to reading researches on carp toxicity levels and found that the acute toxicity level was at 9.0 Ál/L LC50. Translated to ponding lingo-koi will exhibit hyper-excitability at the acute toxic level of about 9ml/1,000L or 35.5ml/1,000gallons, where about 50% of the animals can die.

Armed with this knowleadge, I first tried malathion with my test fishes (3 local koi). I tried several dosages as follows;

1) 2ml/1,000 gallons
2) 5ml/1,000 gallons
3) 10ml/1,000 gallons

For all 3 dosages, I did not observe any excitability given the test kois were in the treated water for 3 days.

I then proceeded to dose malathion to my main pond of wc flashing was then a problem (fish lice present) and found that 5ml/1,000gals best worked for me in the initial 3x week dosing, dropping to 3ml the following 2 weeks. There were no more flashing or jumping observed from then on nor was there any physical evidence of lice. The procedure was to mix the malathion dose in a small bucket of water to dilute it first before introducing to the pond by slow addition and mixing. This is to avoid curious koi from being exposed to concentrated dilutions.

While dosing malathion on the 3rd week, I tried pouring the mixture to my vege filter where my snail pests where multiplying in the white stones. In one hour, the snails dropped from their hold on the stone. However, upon opening the water pumps, I observed the snails crawling happily again on the stones after 5 hours - guess they were just stunned during the initial contact. On the next dosing day, I left the malathion mixture on the vege filter for 6 hours before starting the water pump. This time, all the snails were dead! Talk about killing 2 birds with one stone, huh?

THough I am successful somewhat in my experiments, it would be best for others to use caution if attempting to replicate what I did.

I read in other websites (karl shoeler, koishack forum) where they are testing malathion usage at 2cc/100 gallons. I presume they used 50 to 57% concentration of malathion. At this dosage, its equivalent to 20ml/1,000 gals or double the dose of the experiment I conducted. They did 50% water change after 48hours and re-treated after 96 hours with a water change after the subsequent 48 hours. Hope to see what their final result would be.

As a final note, it will be a 'must' to continuously aerate the pond during malathion treatment as one research indicated that Oxygen consumption can be altered as a consequence of impairment in oxidative metabolism.

Would welcome challenges to my crude experimentation.

Regards to all.


Oct 26, 2009, 3:41 PM

Post #2 of 11 (7517 views)
Re: [lamig747] Malathion - fish lice & snail pests [In reply to] Can't Post

Hi Brother Loren SmileSmile

Many thanks for sharing Brother , ..SmileSmile

Organophosphate is actually Phosphric acid , which in concentrated form , we used it to kill argulus , and it has been more effective against argulus than Dimilin , but it has never been recommended bcos of application and usage . Organophosphate in concentrated form is poured on wall surfaces in the filteration chambers , without the bio-medias or water . The filteration chambers has to be fully drained out before this application , and thereafter we rinsed the filteration walls with clean water thorougly , while we rinsed the bio-mats seperately . This has to be done with experience ..Sly and I can assure you , this do not gaurantee a clean-out on argulus and other parasites bcos of eggs issues ...SlySly . That is why , this practice had been discontinued or encouraged ... Organophosphate if not properly handled , can be dangerous for our kois ...SlySly
Dimilin is a softer and safer approach ...SlySly

I even tried with Cholromine T years back , but the recurrence is always there after a period ....SlySly .
Our water is "living water" and things can disappear today .. and come back the next ... SlySly

Just my 2 cents Brother Loren , Good luck on your experiment Smile



Oct 27, 2009, 2:48 PM

Post #3 of 11 (7448 views)
Re: [DavidSoon] Malathion - fish lice & snail pests [In reply to] Can't Post

Hi Bro,

I agree with you on the danger and need for proper handling of concentrated Malathion. This is one reason why all over the market place, what is available over the counter are the diluted ones of bet 50 to 60%. And even if we apply the diluted version onto the walls, I can imagine the quantity you would require in order to achieve the same purpose as the result of my replicating the recommendations of koi'ists with 2-5ml/1,000 gallons. It will be very laborious just to apply it on the walls (esp if you have bet 20-30% filter area to pond area ratio), potentially toxic to the applicator (this is the worst part) and then having to scrape off the residue from the wall, esp when it dries. Dimilin is safe provided the dosage is followed to the letter, as all other products, THis I guess is where the hazard in using malathion lies as pond usage is an 'off-label' recommendation.

The method I did is more for giving alternatives to koi kichis who need to rotate their parasiticides in order to ensure that they are always effective when used (ie Masoten/Neguvon for 2 weeks, repeated by Malathion for another 2 weeks 6 months down the road, then Dimilin for 2 weeks in another 6 months or when needed). An addiitonal benefit is its widespread availability in gardening shops and supermarkets.

I am familiar with Chloramine T and normally it is used universally as a disinfectant, for eradicating bacterias as well algaes. I have yet to come across studies advocating its use against parasites, what mode of action chloramine t would have in its effect . Maybe at very high doses they can kill, but at the same time it will likewise be toxic against all living organisms in the pond including kois?

Good discussion.



Oct 28, 2009, 7:56 PM

Post #4 of 11 (7357 views)
Re: [DavidSoon] Malathion - fish lice & snail pests [In reply to] Can't Post

Bro David,

I'm just wondering if you use Dimilin religiously in all your ponds? Although I've read all the studies that say Dimilin is safe, I'm kinda reluctant to add anything into the water unless I'm sure it's good for the koi. I believe Dimilin works by inhibiting the growth and formation of exo-skeletons of the target parasites. Call me paranoid but I wonder if it would in some way affect our koi in a similar way? Eg. scale formation? I'm not really smart so I can only make wild guesses.

However, if you use it religiously, I'd feel much safer using it. Since I know you don't have any koi growth issues. Laugh

Best Regards,


Oct 29, 2009, 3:34 PM

Post #5 of 11 (7288 views)
Re: [raistlin] Malathion - fish lice & snail pests [In reply to] Can't Post

Hi Brother Raistlin SmileSmile

They could be time where I shelves my dimilin for more than a year without touching them ...SlySly
Once I find Parasites ( argulus in particular ) in the filter chambers , I get paranoid ...SlySly
Will go straight to the dimilin shelf and administer them to my 4 ponds without having to take a second look on my second pond ...SlySly
bcos , they're all sharing the same "keeper " , same daily water change , same bacteria culture , same build-in set-up , in the same environment ...SlySly
Normally a 2nd dose 5 days later will follow . Normally for the 1st dose , we will see the fishes flashing even worst and sometimes , it will look like they're gonna jump out of the pond ...SlySly
This is bcos , most of the parasites will start clinging on tightly to the fishes when they sense "danger" and this will cause the fishes to react in a crazy manner for at least a few hours ...SlySly
That's why , we would suggest Dimilin be used in the day and Koi-Keepers to stay a close watch on their fishes just in case one or two might really jump out of the pond ...Sly

It's 1gram for a tonne of water dosage that I practice , good enough to kill anchor worm if any ( normally not the case ) , lice if any , and more to eliminate argulus , which is one nasty parasite that can be very scary if you look at them through the microscope ...SlySly comes with 2 fangs and a sting like what you can see in a bee ...SlySly This sting is used to suck the blood of Kois , normally along the gill plate and gills , while the 2 fangs help the parasite anchored itself to the kois ....SlySly . Like maggots that can appear in rotten or decompose flesh , Argulus comes with bird-dropping , and they would normally stay close to water snails to hatch and multiply . These transparent parasite are like flying sauces in shape and can be easily seen sometimes through the PVC pipes in the water when you lift up one ...SlySly . Melachite Green and Bio-tope can never be a solution to Argulus infestation , but Dimilin and Organophosphate ( Phosphric Acid ) can ...SlySly

While we know Dimilin will eliminate exoskeletal parasites , but can the amount or dosage administered be dangerous enough to soften the cartilage or fish bones or structure ??
Some say "yes" while some say "no" SmileSmile.
I believe , anything in moderation , is always safe . Extensive use of any medication or chemicals will never be encouraged ...SlySly
Personally didn't have any difficiencies issues with Dimilin the last few years ...SmileSmile
Though I must add , that I hardly uses them , at most , twice a year SmileSmile .



Oct 29, 2009, 3:44 PM

Post #6 of 11 (7284 views)
Re: [DavidSoon] Malathion - fish lice & snail pests [In reply to] Can't Post

Here is another interesting write-up on Dimilin .
Under the paragraph " Effect on Ecosystem " , you will realised , the dimilin administration or dosage for our ponds , has little or no impact on our fishes SmileSmile.

Hope this help .


P.S - just in case , the Here dun sent you to the link directly , it can be read here : http://pmep.cce.cornell.edu/...flubenzuron-ext.html


Oct 30, 2009, 5:43 AM

Post #7 of 11 (7214 views)
Re: [DavidSoon] Malathion - fish lice & snail pests [In reply to] Can't Post

Bro David,

Thanks for the info. Very educational. I don't really have a problem with parasites right now (I hope!), I was using Dimilin to control my midget problem. Stopped for a while as I was getting worried. Whilst I don't have spectacular koi like some of the bros in the forum such as yourself, I try to provide as healthy conditions as I can to my charges. What would your thoughts be regarding midget control in our filters? Am I asking the right person because somehow I find it hard to think you'd have midget problems. Laugh

Best Regards,


Oct 30, 2009, 8:19 AM

Post #8 of 11 (7195 views)
Re: [raistlin] Malathion - fish lice & snail pests [In reply to] Can't Post

Hi Brother Raistlin SmileSmile

Midgets or water mozzies appeared a while later after we culture bacteria ..SmileSmile .. so they claimed Sly.
True to some extend when I increase bacteria levels , there 's always signs of small mozzies near the " still areas " in our enclosed pond Smile.
Some hobbyists would add stones in the filteration chambers to avoiding having eggs-laying ground for these mozzies , while some would be keeping mozzies-eating fishes to reduce
mozzies issues . Water mozzie issues had been around and discussed umpteen times in this forum ...SlySly

We All , have our fair share of water mozzie problems ...SlySly
I have 4 ponds in my premises ... all close together ..SlySly
If one gets it , it can spread quite easily to the other ...SlySly

Ventilation , even filteration ventilation is crucial in reducing mozzie population or mozzie blooming .
Our filteration covers , are normally wooden planks nailed together , but many do not realised the gaps in-between each piece of wood is importatnt .
It's always recommended to leave gaps of 4-7mm between each piece of wood to allow ventilation .
It helps release the ammonia gas from the settlement / filteration chambers as well .
Mozzie breeds well in still and stuffy chambers , and normally dies off easily when exposed to the sun or open SmileSmile.
It's always recommended to lift up all the filteration covers , rinse and shine them while you're washing the filteration chambers , in the day .
Regular rinsing of brushes will also reduce them drastically . Regular usage of Refresh Powder had reduce this problem , as we believe even the micro-eggs are clustered by the refresh powder and flushed out together and this avoid having them flying off the chambers as adults . A dose of Dimilin , together with Refresh powder , can help you exterminate snail pest , mozzies , parasites all in one ...SlySly , but this is short term solution Smile, but in the long run , preventive measures are encouraged ...Sly

" cleaner water with well aerated chambers " will have lesser of such problems . I have lots of holes and ventilations for my filteration chambers to allow degassing and provide better ventilations and some of the openings allow me to be pouring in water conditioner without having to lift the covers which can be heavy ..SlySly
Will take some photos of my woodden covers to provide some visual ...Sly

Just my 2 cents



Oct 31, 2009, 7:34 PM

Post #9 of 11 (7089 views)
Re: [DavidSoon] Malathion - fish lice & snail pests [In reply to] Can't Post

Hi Abang DavidSmileSmileSmile,

thanks for the very detailed explanation on dimilin use. never know that a second dosage is neededUnsureUnsure.

if we administer dimilin, i reckon we still do water changes. do we need to maintain the 1 gram per ton dosage for the first five days or the whole course of the treatment?
say a 10 tons pond do 10% water change daily, add 1 gram for a 10% loss of strength each water change?

thanks bangSlySlySly.



Oct 31, 2009, 7:55 PM

Post #10 of 11 (7086 views)
Re: [nocternal] Malathion - fish lice & snail pests [In reply to] Can't Post

Adik, first dose 1g/ton, then second dose 5 days later same dosage rate. Nothing in between. Normal flushing continues daily. I believe that should be the treatment. The second dosage is to kill the baby parasites after they hatch, as the first dose will not kill the eggs.

(This post was edited by PH8 on Oct 31, 2009, 7:55 PM)


Oct 31, 2009, 11:48 PM

Post #11 of 11 (7059 views)
Re: [PH8] Malathion - fish lice & snail pests [In reply to] Can't Post

thanks Abang PaulSmileSmileSmile.

my experience when administering first dosage was exactly like what Abang David said. 1 doitsu chagoi was flashing badly, was not before. 1 kujaku jump i think 1-2 feet above waterShockedShocked, luckily in the middle of the pond.
administer 2nd dose 2 days ago, see that they're ok now.
now i'm hoping they will eat more, set a target my other chagoi hit jumbo before the new yearLaughLaughLaugh.
(i know got nothing to do with parasite infestation, just sharingSlySly)


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