Gill fluke or more sinister?

[Squidlet]

Hi all

I have in my tank 3 corydoras(1 albino, 2 julli's), 1 beautiful chocolate strip pleco and 1 angelfish.

Over the last week I have noticed that my Julli cats are not as active as they used to be, they just sit there on the sand or hide, whereas my albino cory is very happy rummaging for food and has grown a lot since Ive had him. Then over the last 4 days I noticed they are both breathing very fast, had fins clamped a bit and just looking unhappy in general. Yesterday I noticed  the bigger one flash a couple of times against the sand, then this morning I've noticed the smaller one flashing against the shale a lot, where as yesterday he wasn't at all. I'm worried they may have gill fluke, although I can't see anything on them that looks out of place. They get a regular water change every week, and I have a water sample I'm getting tested at my LFS for nitrates and ammonia, although the tank is fully cycled so not expecting anything there. Tank is also well oxygenated.

Ive done a bit of a search and found praziquantel mentioned a lot, but no dose rates or dosing program. I have access to droncit tablets and want to start treatment as soon as possible, but don't know how much to put in or when to do a water change etc. Any advice on this?

Also should I only treat the two julli's in a quarantine tank or treat the whole tank? Im concerned about how hard the chemical might be on my chocolate stripped pleco who im very attached to and I'm not sure how sensitive they are?

Any advice is appreciated, thanks