1 dead gourami and 3 dead balas in 24 hrs

Question
I bought my girlfriend a 20gl. tank for her birthday like 10 days ago and some fish 3 2-2.5 inch balas and 2 3 spot gouramis.  All seemed well until about 2 days ago when one of the gouramis got caught in a little pagoda and couldnt get out.  I saw it in time and released him. Since then he was not the same very sullen ad laying on the floor of the tank on his side kinda.  8 hours later a bala got caught in a plant facing straight down and died there I assume. The other fish were acting kind of funny, swimming very fast and then kind of tweaky almost like a seizure. This morning I woke up and the 2 balas that were left were dead.  All three of the balas have had a yellowish-green spot on there bellies in front of their fins  that i had never seen before. The other gourami seems fairly healthy? My neighbor has some drops that he added at when we set up the tank "to get rid of toxins".
Basically what killed my fish and how do i fix it.

Thanks a ton.
Adam

Answer
Hi Adam, this could be a number of things but the main thing that could be wrong is the water quality levels may be high in your tank throwing everything off. My suggestion would be to bring a sample of your water to your pet store and they will tell you exactly which water quality levels are off and show you which chemicals to use to fix it. I personally have never ran across the problem you have but if i can be of any more help let me know. Sorry for your loss, good luck.