What is the easiest way to fix a loose chain?
Are there adjustments that can be made instead of replacing it?
It depends on what you mean by 'loose'... Chains stretch naturally over many hundreds of miles, and the stretching of the links is actually a good indicator of wear.
If, instead, it seems like there is a lot of slack or 'extra' chain, this is an indicator of one of two issues:
- The chain is simply too long. All new chains (not already on bicycles) come longer than they need to be. If you recently replaced your chain, and didn't remove the extra links, this would cause the chain to be loose.
- The dérailleur is not creating chain tension. If you find that the chain seems to sag at both the top and the bottom, this may mean that your dérailleur has lost some of it's 'springiness' and is not effectively creating chain tension. It's hard to determine without further details, but if this is the case, the dérailleur may need to be replaced.
To amplify the frist part a bit, if it was once fine and is now slack/loose then replace it - there's no reason why it has to be a particularly expensive for a upright (slightly different for the 2.something chains needed for my recumbents) and its an easy job to do - even more so with contemporary chains with clever links. When doing the replacement compare the old and the new and you'll see how wear has caused it to "stretch". In theory you're supposed to replace other stuff too... but that does get expensive.