Owen has sore feet

Poor Owen, his skin isn't totally better and now he has thrush in his front feet. It is in the heel of the foot/frog and it has got sore enough that he was limping. We called the farrier and she pointed out that the groove in his heel is much deeper than on the back feet and said this is caused by the bacteria and fungus/yeast or whatever thrush is. So now we are treating his feet everyday with neat hibiscrub (antimicrobial used by surgeons). We are cleaning out the groove thoroughly and then using a syringe (without needle) to get it right in there. The limp has gone away after a few days of this treatment, but we need to keep it up so it doesn't come back. We may also start painting his soles with something called 'Le Goudron de Norvège' or in English 'Stockholm tar' (yes Stockholm is not in Norway, no idea why the different countries called it those things - it is also called pine tar and was originally for waterproofing wood, like creosote)
The picture is not very clear, but the circled area should be 'concave like the bowl of a teaspoon' rather than swollen shut to a narrow groove like it currently is. 
We are learning more as we have different problems, but poor Owen has suffered a little through our ignorance.