質問: I believe these are both grammatical, is there a slight nuance difference for not having を?: 私は毎日三十分ぐらい運動をすることにしています。 And 私は毎日三十分ぐらい運動することにしています。
回答: As you said, both are grammatically correct. One difference I can think of is that adding 「を」 makes it more formal. Keep in mind that there are some situations in which 「する」 can't be used but 「をする」can, i.e 祭りの準備する(X)祭りの準備をする(O). It really depends on what precedes it. Placement of 「を」 can also be used to emphasize, but that's irrelevant to this question so I won't get in to it.