There are smarter people than me here who will do better, but if you are using the same rear derailleur, if you have a smaller small ring, it would account for the slackness.

if you search online for “sizing a chain”, you can get rid of the slack by removing a few links.

sheldon Browns website is enormously helpful about all things bicycle.

PS
1. tighten cables when they are in the small sprocket position (parallel to the down tube). Any slack is likely to be pulled by the derailleur springs
2. You might want to list the components and let the resident gurus check compatibility with crankset, chain line and shifting. Friction will shift anything but chainline is important.