Catching wild fish for the tank.

[duanes]

At 5 weeks, your tank might not be sufficiently cycled enough to be adding more fish.
The mollies may be dying from ammonia poisoning if enough of the ammonia consuming bacterial population is not large enough. At this point , I'd be doing 50% water changes every day.
Of course most wild fish are infected with a few parasites, and in nature these parasites are mere irritations, and because of space they do not reach epidemic levels, but in the confines of a small aquarium, with there's no where else to go, these parasites infect, then reinfect, and reinfect again, attaining overpopulation levels, becoming lethal.

 

[duanes]

At 5 weeks, your tank might not be sufficiently cycled enough to be adding more fish.
The mollies may be dying from ammonia poisoning if enough of the ammonia consuming bacterial population is not large enough. At this point , I'd be doing 50% water changes every day.
Of course most wild fish are infected with a few parasites, and in nature these parasites are mere irritations, and because of space they do not reach epidemic levels, but in the confines of a small aquarium, with there's no where else to go, these parasites infect, then reinfect, and reinfect again, attaining overpopulation levels, becoming lethal.
In my video below, you actually see parasites living on the catfish in a Cenote in Mexico.
Cristalino

 

[Deadliestviper7]

Everything in my tank is wild. Tank has been set up about 5 weeks. Recently started doing 30% water changes twice a week after 3 mollies died within days of each other. Nothing shows symptoms until they go lethargic on the bottom and kick off. I see no signs of ick.
Should I treat the whole tank?

I've found with mollies the most common reason for their death is people forget they aren't freshwater fish

 

[Deadliestviper7]

Everything in my tank is wild. Tank has been set up about 5 weeks. Recently started doing 30% water changes twice a week after 3 mollies died within days of each other. Nothing shows symptoms until they go lethargic on the bottom and kick off. I see no signs of ick.
Should I treat the whole tank?

I've found with mollies the most common reason for their death is people forget they aren't freshwater fish

 

[Kris P Bacon]

I've found with mollies the most common reason for their death is people forget they aren't freshwater fish

I hear they live in anything from pure fresh to pure saltwater. Should I add salt? They were caught 38 miles upriver so I suppose it is brackish to a slight degree.

 

[Deadliestviper7]

I hear they live in anything from pure fresh to pure saltwater. Should I add salt? They were caught 38 miles upriver so I suppose it is brackish to a slight degree.

That slight salt is vital to reliable health, you can just add a little seawater or marine salt

 

[thebiggerthebetter]

Everything in my tank is wild. Tank has been set up about 5 weeks. Recently started doing 30% water changes twice a week after 3 mollies died within days of each other. Nothing shows symptoms until they go lethargic on the bottom and kick off. I see no signs of ick.
Should I treat the whole tank?

Hey neighbor, I was reacting to your idea of taking the little plecos to an LFS that they would have to be treated in this case. Unless LFS would take them in untreated and treat them themselves.

 

[Gill Blue]

Recently started doing 30% water changes twice a week

The fish would do better with 80%-90%. Once a week after the cycle is going, two to three times a week until then.