Trtmt For External Parasites

Anyone treated successfully for external parasites and, if so, with what medication?  This https://forums.thinkfish.co.uk/fish-medicines/ is a great resource but treatment for external parasites has not been mentioned - has anyone ever tried any?

This morning while observing the fishtank, I noticed a green neon rasbora brushing along the tank substrate. Ordinarily, the neon greens are in the upper echelons with the harlies but this one seemed to be cavorting with the x-ray tetras. I wondered if perhaps it had started hunting for superfluous food on the substrate. However, it's clear now that it is ill - pale, darting around, rubbing its pectoral area in the substrate, then flailing and hitting itself off the glass from one side of the tank to the other, etc. I'm not seeing anything else untoward on its body (eg flukes, spots, protrusions or from its vent even when it does have a moment of being still to catch its breath). I'm assuming, though, this might require some sort of parasitic treatment.

The 50% weekly water change and water quality monitoring has been delayed by a day so far (as I've acquired a cold and am sneezing and my nose is dripping like a tap) but the tank is only 67% stocked so I wouldn't have thought this delayed water change was the cause - and I've steered clear of meddling with the tank due to my cold.

A 'good news' update. I decided that, as my nose and sneezing weren't in as bad a way as yesterday where the dripping and sneezing were respectively incessant, that I could probably 'control' the situation by attempting a water change with a few adjustments ie mainly avoiding leaning over the tank at all. What a difference this made! The little green neon stopped flailing around immediately and shoaled up with its tankmates throughout. As soon as the water change was complete, he was back to his normal colour and up in the upper echelons again, behaving as though nothing was untoward at all - and this has remained the case for the past hour. I had been certain that I'd have a fatality on my hands today, whether I quarantined or treated him, but this transformation from a simple water change is looking very promising... fingers crossed it's not one of these false-hope 'sudden improvements before the inevitable' scenarios.
Water quality was its usual 0,0,~20, so it would appear, as has been said before, that these neon greens are particularly susceptible to any dip in water quality, even from a one-day delay in fishtank maintenance and which isn't even perceptible on water quality tests!

Update: By the time I finished this post, and went back to check the tank again, it looks as though my comment about a false-hope reprieve was indeed that - he's resumed his flailing behaviour.    While watching him, the light came on, and I see it's the last of the original 8 of these fish that I bought a year ago - one which had a characteristic sharp forking in his tail...  Suffice to say, I don't think I'll be getting this species again as they haven't done very well although I still have 3 of the 4 newer ones (after one took a fatal leap a while back).

External parasites covers a wide range, from whitespot and velvet (protozoan parasites) though skin flukes and gill flukes (types of flat worm) to anchor worm (actually a crustacean despite the name) and fish lice.

From eSHa's range of meds:
whitespot/velvet - eSHa Exit
flukes, skin & gills - eSHa gdex (also treats internal tapeworms, which are flat worms)
anchor worm & fish lice (Lernaea and Argulus) - eSHA alx




I have also added extrenal parasites to the thread fcmf mentioned