Ok, so probably not carbonic bite.
What is your water like initially? 1 gram each of CaSO4 and CaCl seem like really small amounts to me, but I start with really soft water so it's possible it's putting you over some flavor threshold. Though I've had a lot of over-mineralized beers in local competitions from people trying to bump our soft water up to match famous brewing waters, and none of them seem especially grapefruity or citrusy to me.
For my last batch of pale I added to the mash 1.5 grams of MgSO4, 2.25 grams of CaSO4, and 3 grams each of CaCl and CaCO3, nothing to the sparge or boil. It turned out really nice, but like I said, we have really soft water.
I'd lean towards something else - how often have you used magnums?