I treated for ick last night with spots only on the fins and today, it had spread

Sorry didn’t take a picture of it I am kinda having a bad day we have had a tank for 2 months everything’s going well so far till today,
we have a female betta with 6 tetras. Had some shrimp have not seen them.
It is a 10 gal tank.

But today I noticed one of our tetras had died over night.

There were some nibbles off of the one that died.

The other fish seem well and I did not see anything on the fish so I am assuming this is more of natural life. But my heads over thinking if I need to do anything to ensure the safety of the other fish.

The only thing would be is our water currently 7.5 ph with some film on top.

We just have a hang on back filter but the filter is just a hard porous sponge with a softer sponge like one on top (it’s what came with the tank)

Other question is with schooling fish if I need to replace the one fish to be 6 or if it doesn’t matter: