Will this work transferring tanks to smaller

[Samanthabea]

I had recently got a 55 gallon tank the fish are dying from ich started with 8 mollies 2 platties and 5 tetra a pleco and 5 ghost shrimp now I have 4 shrimp 1 platty 6 mollies and 4 shrimp I'm trying to downgrade the size of tank I took the water and both filter media(set inside the tank because it was to large) to the smaller tank to keep the bacteria alive and switched that tank to fluval stratum soil so I could eventually add real plants, take away any ich eggs from the gravel and it's better for the shrimp, is this the way to do it and is there anything I'm doing wrong or missed as for the ich I'm still fighting it another was lost today meds heat and salt hasn't worked so far it's been a week