Sorry if this is the wrong section, I couldn't find a disease section, but I may not have looked hard enough.. I just found it, so can this be moved please??
So about a week ago, I was feeding my 150g freshwater and on my 7 year old Silver Dollars, I noticed what appeared to be ich. I decided I'd check my aquarium salt level and do a water change and get my salt level to the appropriate level. I've always been under the impression that a healthy amount of salt in freshwater is the best way to avoid ich, along with quarantine which I'm sometimes lazy on... But anyway, in the past week, I've lost all three of my 7 year old Silver Dollars, a Featherfin Cat I've had just as long, and my Smallmouth Bass had been sick until yesterday. I work 10 hours everyday so Sunday night was when I was finally able to get Ich treatment and put it in the tank, ad I added the second dose this morning. In the tank I have a Florida Gar (moving to a 250g once he's bigger and I can find one cheap), Rocket Gar, a Placo that's about 10 inches long, a large Tinfoil Barb, a younger Silver Dollar, Smallmouth Bass (moving with the gar), and previously the Silver Dollars and Featherfin.. Why were only half of the fish affected? Were the healthier ones just able to fight it off? And how come the bass seems to be the only one able to have recovered after getting it? I haven't added a fish to the tank in probably six months, so where did this come from? The only reason the fish that died were even moved into here was because they outgrew their 55g years ago so I've never been able to make this a piranha tank like I planned originally.. My tank stays at 78 degrees and I put it up to 82 to try and speed up the ich life cycle. No ammonia, no nitrite, and my nitrate fluctuates from 0-10ppm. If anyone can help me figure out what happened or how it happened, and how to avoid it from happening again, I'd very much appreciate it and I'm happy to provide any information I may have left out that's important.
Also, on the glass toppers I found small bugs? But I've had saltwater ich before and I am fairly certain that this is not what was killing fish.

So about a week ago, I was feeding my 150g freshwater and on my 7 year old Silver Dollars, I noticed what appeared to be ich. I decided I'd check my aquarium salt level and do a water change and get my salt level to the appropriate level. I've always been under the impression that a healthy amount of salt in freshwater is the best way to avoid ich, along with quarantine which I'm sometimes lazy on... But anyway, in the past week, I've lost all three of my 7 year old Silver Dollars, a Featherfin Cat I've had just as long, and my Smallmouth Bass had been sick until yesterday. I work 10 hours everyday so Sunday night was when I was finally able to get Ich treatment and put it in the tank, ad I added the second dose this morning. In the tank I have a Florida Gar (moving to a 250g once he's bigger and I can find one cheap), Rocket Gar, a Placo that's about 10 inches long, a large Tinfoil Barb, a younger Silver Dollar, Smallmouth Bass (moving with the gar), and previously the Silver Dollars and Featherfin.. Why were only half of the fish affected? Were the healthier ones just able to fight it off? And how come the bass seems to be the only one able to have recovered after getting it? I haven't added a fish to the tank in probably six months, so where did this come from? The only reason the fish that died were even moved into here was because they outgrew their 55g years ago so I've never been able to make this a piranha tank like I planned originally.. My tank stays at 78 degrees and I put it up to 82 to try and speed up the ich life cycle. No ammonia, no nitrite, and my nitrate fluctuates from 0-10ppm. If anyone can help me figure out what happened or how it happened, and how to avoid it from happening again, I'd very much appreciate it and I'm happy to provide any information I may have left out that's important.
Also, on the glass toppers I found small bugs? But I've had saltwater ich before and I am fairly certain that this is not what was killing fish.