What’s your recipe for borax Pete? I find that if there is a better food source, they’ll go for it rather than borax. I wish it worked as I hate using poisons.
All the ant dusts I came across here in WA are contact killers. It usually kills a few ants but they will just pop up elsewhere (you think they’re gone). Their active ingredient is either Bifenthrin, or Permethrin. Using them carelessly will increase resistance in target species, and you also kill non target species including beneficial fauna in the environment. They are extremely toxic to aquatic life.
When I really have to use a toxic chemical, I use Amdro https://www.bunnings.com.au/basf-amdro-170g-granular-ant-bait_p2963666.
Rate is only 5g per 20m2.