The organophosphate Trichlorfon (Dipterex, Masoten, Metrifonate, Dylox, Negavon are all the same thing) is used quite frequently in koi keeping because it is very effective against various flukes (both gill and body fluke), fish lice, anchor worm, Ergasilus.

Also Cestoda (tape worms), Hirudinae (leeches) and snails. In short, most insects will be killed. Good thing is it degrades quite quickly in pond conditions. Bad thing is it will cause disorientation and nervous disorder if used incorrectly.

Typical symptoms of overdosing in koi is a bent spine and nervous, wip-like swimming. The fish may recover over a period of a year or two, but no guarantee - but try selling a pond of overdosed fish like that will cause a headache. Always weigh or measure your pond medication correctly.

The following Dipterex treatment is valid for koi and goldfish:

1 g/1000 liter in water of average total hardness

0.5 g/1000 liter in soft water like the Western Cape.

You can use it with salt. The combination of Trichlorofon and salt (3kg/1000liter) is a very good “first treatment” after harvest.

Once opened store in a dark, airtight container. Do not use it when it old (it looses it's bluish colour)


Do not use below 18 deg C (fish cannot metabolise/excrete it fast enough)

Do not use above 28 deg C (uptake rate is too high)

It is toxic to sharks (tropical fish)

It can be removed by activated charcoal

It is always good to give a follow-up treatment a week later.

Do confirm the concentration of the active ingredient (Dimethyl 2,2,2-trichloro-1-hydroxyethylphosphonate) of your product bought. Content should be 970 g/kg (97%). Adjust the dosage accordingly.

Be very careful when usung the neat product. Wear gloves and mask - as you do with all other chemicals.

About warm water aquaria:

My experience is only with koii, but my gut feel is that this temperature sensitivity to Dipterex is the reason that warm water aquaria has problems with it. The rate of metabolism varies with fish species. So working with this knowledge one can still use it quite effectively. If you want to kill gogo's like leaches and snails and water beetle etc in your tank, remove the fish to another tank (at same temperature) for 24 hrs. But if you want to treat for things like fluke or worms that are on the fish, move the fish into a clean tank, no gravel, no filter, only air, but clean water at same temperature, for 4-6 hours, and move it back to its home after treatment.

Servaas de Kock