If the leak was quite soon after filling the barrel and the brew hadn't been in there very long then there is usually no need to add more sugar, if it has been a couple of weeks or more then you could add another 30g or so of sugar just to help it carbonate and re-pressurise quickly.
If the barrel contents are half way or well down, then inject a CO2 bulb in if you have a brass valve fitted and this will displace any air quickly too
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If the barrel contents are half way or well down, then inject a CO2 bulb in if you have a brass valve fitted and this will displace any air quickly too
Many Thanks for your help
Bacon