Too Much Conditioner?

Had two college guys come into the store to buy some goldfish.
As apparently they'd bought a tank and a fish...but it had died right away.
So after getting new fish, 
They came to me, wanting to make sure they'd bought the right kind of water conditioner for their tank.
As they were wondering if they bought the wrong kind and that's why the fish died.

Nope. They'd bought the right kind.

However.
After talking to them I discovered that their tank was maybe around 3 gallons, judging by the approximate size they were indicating their tank was.
And I asked them how much water conditioner they'd placed in the tank.
Because putting too much in can often kill the fish. 

Yah.
The dude said that he'd poured in like...half the bottle.

Considering one full bottle can treat 230 gallons of water....
Half a bottle at 115 gallons into a 3 gallon tank.....
Yah....you killed your fish from overtreating the tank. *shakes head*

The dude didn't even think to read the directions.
So I corrected them, and told them to only put in a few drops.
Because like 5ml will treat 10 gallons. So you only really need like 1ml or so for the little 3 gallon tank. 

*fingers crossed* that they don't kill their new fish right away.
I did tell them to change out like half the water to get the water levels down.
So hopefully that helps.
Hopefully.

-Sarnic Dirchi