Hi there,
Yes it absolutely is possible to provide too much calcium in the diet, if we are providing synthetic D3 in the form of supplementation. The excess can range from low level to a degree of buildup within areas of the intestinal tract resulting in hindered absorption of key nutrients among many other far reaching consequences.
As for how can we tell? In short, without blood work in the form of a mineral & vitamin profile, we cannot. For that reason it is best to err on the side and caution of restrict calcium 'rebalancing' to light dusting of insect prey exclusively.
Guesswork based practice such as adding pure calcium to intended gut-load is a very risky business and is not something I could ever recommend in these cases. It is far better to provide feeder insects with a well balanced and varied diet and then lightly dust those insects at the point of feeding while following a well thought out supplementation regimen.
In other words, dust appropriately and do not engage in any other form of direct calcium introduction if you are not allowing self-production of D3 via measured provision of UVB.
