Sherlock's stools also follow this pattern - reassuring to hear it's so common!
I did take him to the vet as I was worried, and the vet gave him a strong wormer which made him worse for a few days, and now he's back to how he was before, so it didn't do a lot of good. I am trying around with different foods to see if there's one that suits him better. So far Chappie wet has been the best, but I don't think it's a particularly good food in terms of ingredients so I'm still looking. Arden Grange kibble made it worse, both the normal and the sensitive range. I then tried a duck and potato kibble, I think it was called Milburns, which also didn't help. Maybe it is just a lively cocker spaniel thing?