Overzelous Treatment Caused Permanent Harm?

[CluelessAboutFish]

Water Parameters:
Ammonia 0
Nitrite 0
Nitrate 0
PH 7.2
Temp 78
Alkalinity 6

After fishless cycling my 29 tank, I added a dose of aquarium salt (1 Tablespoon / Gallon) and about 14 platy. I added the salt because I read it helps reduce stress. I also added a half dose of QuickCure for 2 days. This is per the instructions on the aquariumfish.net site. Then I noticed that a few of the fish had frayed fins with gray on the edges. Thinking it was fin rot I added a dose of Melafix. The problem is that I misread the label and added 3 tablespoons instead of 3 teaspoons. Over the next day I lost 4 fish. After realizing my mistake, I did a 50% water change (with salt to maintain the theurapeutic level). I have since lost 1 more fish.

Now at least 4 fish have a slightly clamped top fin (laying back rather than sticking straight up like the other fish). In every other way, they appear fine and are still eating and active.

So I have completley overstressed and overmedicated my new fish. Should I do another water change, or will that stress them out too much? Have I permanently damaged these guys? Will they be dropping like flies over the next few weeks/months? When adding new fish, how long will they show signs of stress?

 

[KathyM]

Water Parameters:
Ammonia 0
Nitrite 0
Nitrate 0
PH 7.2
Temp 78
Alkalinity 6

Putting the meds problems aside (others have much more experience than me in that), your tank doesn't seem to be cycled, or it would have a nitrate reading.

 

[WILDER]

I agree with the nitrate reading, need to look at your tap nitrate reading.
Yes clamped fins are a sign of stress and desease.
The fish have been overdosed so it hard to say if you will lose anymore fish, it down to them now.
Remove the med completely, do a water change and run some black carbon.
Salt might help.