Water Conditioner Over Dosage

My son watched me do a water change for the first time today, of course I took the water conditioner out of the cupboard, add it, put it back and walk away. I return to the tank and my son has the bottle of conditioner empty in his hand. His response was "I am helping 'red' have good water." I took the 3 fish out right away and now am afraid to put them back in. How long should I wait or should I just start from scratch and do another water change?

 

I dumped a brand new bottle meant to treat 1000 gallons into my 20 gallon tank. Fish were fine. I wouldn't worry about it.

 

Thanks! Our tank is 20G also and the bottle was half empty. So I should be fine to put them back in their home?

 

I wouldn't worry about it. In my case, I accidentally bought water conditioner thinking it was a bottle of tetra safe start (lol). With safe start you're supposed to dump the whole thing and then leave it for several days....so I did. Didn't even realize what I did until like 4 days later, and the fish were just fine.

 

What type of water conditioner?

 

Top fin betta water conditioner. There is a betta and 2 cory in there.