if you cleaned the tank and changed the filters you killed your beneficial bactieria or at least a large amount of it. This will cause a spike and that will cause fish to die. If this is the case I highly suggest you get them in another tank "hospital" tank and out of that water asap. Now the tank they go in will need to have water from a good tank... dont put them in 100% new water otherwise it will go through a cycle and kill the fish.
As in I had a tank spike once... so I used a spare tank and added water from a different tank (one that water paramaters were good on) along with some new water from the tap, treated it and added the fish and used a filter off one of the other good tanks on the hopital tank.
Not sure if this will help if you dont have other tanks to use. In that case test for ammonia and treat the ammonia asap. Thats all I would really know how to do. I dont know what happened with my tank but I ended up having to tare it down, keep all the fish in a holding tank and re-start my large tank from scratch. (Hopefully that is not the case for you)