Invertebrate parasite treatment for fish and aquaculture
Trichlorfon is not available in outh Africa. It is listed/registered (Metrifonate, (2,2,2-Trichloro-1-hydroxyethyl)phosphonic acid dimethyl ester,) but seems generally discontinued. Pesticides and insecticides such as trichlorfon, dimilin and Diazinon can impact wildlife such as bees and other insects.
Once commercial alternative is praziquantel (Liquid PraziPro).
Two less-environmentally hazardous products that are used to treat koi parasizes are Halamid (Choramine T) and Potassium Permanganate (KMnO4).
See this article on the use of potassium permanganate in fish ponds for koi, goldfish and other fish.
Another product suitable for some parasites is Halamid (chloramine-t). Chloramine T is a fungicide, algaecide, antibacterial/germicide, and virucide, so it helps to both treat and prevent a host of issues both inside and outside of ponds. In aquariums, aquaculture, and ponds, chloramine-t is most often used to treat bacterial gill disease but is also utilized to treat gill and skin flukes, fungal infections, costia, chilodonella, trichodina, and is particularly effective against myxobacteria.
See the Chloramine T usage guide.
See also, a general review on ectoparasites is the 2019.
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.
About warm water aquaria:
This document is for koi fish. 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 organisms like leeches 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.