Just to add my two pence worth... ...

I feed mainly on mice/pinks alternating with trout...and the odd worms for a treat..but I rarely use calcium unless they are not eating the mice....

If a garter snake in the wild saw a worm, a slug or a tadpole, it wouldn't stop to find its calcium salt shaker....it would just eat it....

what I am trying to say is do not worry too much if you are feeding a varied diet,
only if you are only feeding fish or only worms would I add a suppliment.

be careful because I think the opposite is just as harmful, you can add too much vitamin