Keep at it until the tensioner runs out of stroke OR, the first chain breaks, then replace them all.

First replacement of chains - swap drive sprockets side to side, replace idlers with new ones with grease fittings if not factory equipped.

Second replacement - replace chains, drive sprockets and idler sprockets. About that time, deck plates and snapping rolls will likely be in need of attention.

That's our experience anyhow...

Ken