Bouncing numbers, but can't reduce insulin down

Have not posted for a while so please bear with me.

As of mate, Shadow is currently on 3 units of Caninsulin every 12 hours.

Sometimes he goes into green numbers in the evenings.

He always bounces higher just before insulin times.

He weighs 6.3kg.

He also has Stage 3 Kidney Disease, which vet believes to be the cause of the diabetes.

I've tried to lower his dose, but when I do he "bounces".

He's on wet food only, which are also low carb and low phosphorus.

Thanks.