Returning To The Hobby After 40 Years, Problem With Ox In Tank

[Mnodak]

Recently build a new 20 gal cichlid tank.  Everything was fine for the first 3 days, then 2 fish died, both from same family.  They would sink to the bottom, appear dead, then move like a bullet for 3 4 inches and drop to the bottom.  Eventually they died.  Know al the rest of the fish are glupping air at the top of the tank.  Any suggestions, thanks
 
Mark

 

[Ninjouzata]

What type of cichlids?
Only smaller ones would be suitable for that size tank.
Did you cycle the tank? What are your water parameters?

 

[Blondielovesfish]

What are the ammonia and nitrite readings?
 
What types of Cichlids do you have in your tank currently?