beta was inside the filter system 45gph My granddaughter has received a beta fish ..half moon . Now I get to care for rainbow ... I have a 3 gallon tank with a 45gph filter.  With a cover on the tank with LED lights ...I used bottled water   Let it sit overnight and then introduced rainbow   All was well ... Until I noticed the beta kept going near the top of the filter n lying on it  weird ?   This morning no fish in the tank .... So I removed the top of the filter and the beta is in the filter !!! Beta jumps out thankfully into the tank ... Looks a bit sluggish !   I lowered the water level but not sure if filter will work if water level is lower and I'm stressing about a beta !
What am I doing wrong ?  What should I have in this round pretty tank ?  Is the tank wrong. Is the filter wrong ?  I need help 