I agree with Anthony .I am no expert but I would also add that you need to think hard about the reason why you are pre baiting / groundbaiting . The main reasons as I understand them is variously to attract fish in to the swim , to encourage them to stay , to get them used to your bait , become pre occupied with feeding and thus lose caution and take your hookbait . My view is that many anglers overbait with filling examples of their hookbait , with this approach the barbel may get used to the bait and lose caution , but they may also eat it all , become full and clear off to sleep it off as it were ! Keep them lean and keep em keen is my view , over feeding is very easy to do . I think some anglers over feed as it psychologically makes them feel better . If you want to chuck things in make sure its none filling like hemp / maggots etc , these will attract barbel [and often everthing else that swims] in and retain them but unless you actually throw tons it is difficult to over feed . I am a great believer in using single high attractant hook baits with minimal free offerings .I also think it is also well worth trying natural baits like black slugs , lobworms etc particulary in coloured / high water , after all this is what barbel spend most of their time eating , although I do accept that in rivers where the barbel see a lot of pellets going in they do see the pellets as normal ' natural ' food