Question about lifecycle of parasites and treatement thereof?

[Blue Fish]

Okay, I posted this a bit back...and I seem to have narrowed down their mystery disease to gill flukes...but, how on earth did they ge them?!?
This is really bothering me as I want to make sure that it does not happen again.

They (six fish), two in separate ten gallons, two in a divided twenty gallon, and two newer ones who're still building muscle before they can handle the larger tanks, living in 2.5 and a 5 gallon. All will eventually be in divided twenty gallon tanks, 10 gals per fish. All tanks are heated, but even with sponges I can't get the filters de-flow enough to keep them happy, so I change 50-75% of their water every seven to ten days and have ceased to use the filters. (Yes, it takes hours in such big tanks, but you have pets then you commit to taking care of them). They are big, very big, nice long fins, clear eyes, swim around a lot, flare at one another, eat voraciously, very happy fish. Then, out of the blue, one of them gets sick. I've had him since march, he was a large adult when I bought him, so possibly he's older, but very large and very healthy.
He came from Petco, had ick within a few weeks of purchase, treated with (cringe...) coppersafe...and cleared it up quickly. No further problems other than a minor case of fin rot, treated with frequent water changes and a low-dose of jungle fungus clear (good all-purpose). Tried salt but he can't handle it for whatever reason.
(He starts breathing heavily, even dissolved first and acclimated.)
That's been a couple of months back. Healthy since then.

Then, a week ago, he starts laying on the bottom of his tank, gasping for air, obviously having some issues. I finally narrowed down his symptoms to gill flukes. But how in the crap did he get them?!
He lives in his own ten gallon (he and another have a divided twenty, but the tank is new and the boys have not yet started living in it yet, was going to put them in but he got sick just after, and didn't want to expose the tank-mate), no new plants, no new ornaments, no new food, no new fish...nothing. He just starts having issues. I mean, seriously, HOW is he getting this?

I know that flukes are a parasite...and parasites can exist even in healthy animals, and must be treated either with natural treatments (like garlic) or with meds to get rid of them. It's not a matter of then being healthy enough to fight them off, parasites are there until they are killed off.

So, could he have been harboring the flukes all this time and after his water change he was stressed and they had a "bloom" due to his weakened/stressed state? I change water frequently...and the fish do not seem overly stressed by it. I cup them out, put them in a gallon size bowl in a dark room with their own plants, clean the tank, refill, condition the water, and then acclimate them to the new tank/temp/water parameters over a period of a hour with slow water additions to their floating cups in the big tanks. They swim around and seem happy immediately and eat well directly after tank changes. I'm sure that they are moderately stressed, but they don't seem to be overly stressed, especially as this is a common occurance for them.

But, for that matter, how did the flukes survive the coppersafe and/or the jungle fungus cure (which has ppm...to kill parasites...)? Do they have a life cycle, and the meds are only effective for *part* of that cycle, so if you don't treat in the right cycle and get them all, they're still there?

The other fish who is affected was almost boiled one evening due to a faulty heater (please don't scold me, I felt terrible...I got new adjustable heaters and for whatever reason overnight the thing took the temp up to almost 90...) I went to feed them and Geoff was gasping on the bottom of the tank, obviously trying to find cooler water, and Chaucer was lethargic and near the surface. The next day Geoff started showing the same fluke symptoms, and I'm sure it was due to the stress of the near boiling. So, again, another stressful event and then a "bloom" of parasites.

I'm treating currently and both seem to be recovering, but I'm curious as to how this has happened so long after coming home from the pet store. I always worry since they do come from petstores, so I'm sure that they have some genetic issues, probably several parasites, and are more disposed to disease...but I rescue them from their tiny cups and give them good lives, it's worth it to me to do whatever I can to help them for however long they live.

Also, I feed them freeze-dried bloodworms...could there be parasites in there? I know that mosquito larvae can harbor several types of parasites, so could this be the culprit?

Any information is appreciated. I'm curious as to what's going on here. :)

[ChoclateBetta]

Parasites like ick reproduce faster in warm water most medicine target them in there free floating stage also many freshwater parasites are more sensitive to aquarium salt than most fish. Things like scaless fish do not do well with medicine like salt and copper same with inverts. On the flip side many scaless fish are less likely to get the parasites in the first place.

[Oldfishlady]

As you already know......Flukes like most parasites are always on the fish in low number and the fish will not be symptomatic, however, once the fish is stressed and immune response compromised the parasite can take advantage. Parasites don't want to kill their host-without them they will die too-usually it is a secondary infection that kills the fish-not the parasite per se. Sometimes it can be the treatment itself that ends up killing the fish-not the parasites....Then you can cause resistant issues with overuse and/or treating the unknown.

With gill flukes-they can bury themselves in the gills and be protected from chemicals used. Total eradication can be impossible with most parasites both internal and external.

[Blue Fish]

So if the suckers can get in there and be buried...is there anything that can be done? The fish are large and healthy, their tanks are cleaned frequently, they are kept warm, they are fed blood worms, brine shrimp, and NL spectum pellets...I don't know what else I can do to boost their immunities/better their health. (tanks are unfiltered, but ammonia levels are kept very, very low due to frequent water changes and almost daily tank vacumming.)
Are they just doomed? :(

[Oldfishlady]

No, not doomed....both external and internal parasites are normal to some degree in all our fish-by supporting or providing the tools to the fish that support immune response-they will take care of it themselves....

[Blue Fish]

Okay, so I'm ready to re-try the salt treatments...He had a bad reaction to them before (serious breathing issues) but maybe if I tried a lower dose?

And with AQ salt or epsom salt, is one gentler than the other? I used AQ salt previously, but I have both.

What about salt baths...would that be effective as an alternative to salting the tank?

Thanks for your help...poor little guy. I don't want to give up on him...but I don't want to kill him with the cure either. :(