I made my first batch of hash brownies for my husband yesterday. They turned out pretty potent, and he really enjoyed them, but he got a stomach ache.

I added 8 g of water hash to the 1/3 cup canola oil the recipe on the box called for. The 8 g of hash made 8 servings in a 8x8 pan.

I did not heat up the oil. Does the oil need to be heated when using hash?

Was a gram of hash per serving too much? He's got a high tolerance.

I use 8 grams of shake for mine which seems to be pretty potent to me. 8 grams of hash would be really potent. Some people do not tolerate edibles well because cannabis has millions of little spurs. But doing the hash route should have removed all that.
Did he eat them on an empty stomach?

I think he did. I think I'll try the recipe again, only this time make hash butter.