If the protein source is from cereals (which are quite indigestible to a dog) then this can cause hyperactivity and fizzy behaviour- I think it's something to do with starch if I remember rightly. If the protein source is from meat (very digestible) then it will pass through the system and not cause adverse behaviour. Our 2 are fed Millies Wolfheart, the protein levels are high but the food is grain free and thus doesn't cause problems as the protein source is quality meat (not derivatives).
I would disagree with not feeding working dog food to pets- quite often it is the same food, just packaged differently, to avoid VAT. Milies Wolfheart is a working dog food but our 2 sprockers do very well on it.
Dr Johns is pretty awful as a food- look at the list of ingredients- if it contains cereals listed first, meat derivatives... say no thanks and find something else. Skinners is a good mid range food but we now feed grain free Millies and have seen a huge difference in the condition of our 2 girls.
Spaniels need a lot of mental stimulation, we have 2- mother and daughter. The mother is 6 and quite happy to bumble along in the tractor but the daughter (3) is a product of her Cocker father and quite honestly mad as a box of frogs
but I wouldn't be without either of them.