Calcium and axolotls?

So recently I've noticed during water changes that the water comes out of the tub (I fill the buckets in my tub, not with a hose or the sink since my tank is large so I use larger buckets) milky. It takes only a minute or so to clear up and when it does there is no residue on the bottom or sides. I googled it and found out it could be one of two things:

a) excess oxygen that is dissipating, typically happens with lower temps (so lotl temps) and clears quickly and leaves no residue, obviously.
b) calcium, which apparently some tap water is treated with it (not sure if it's mine, when i goggled it I clicked the first result so it could have been for another state). the website said that calcium takes about 30 minutes to completely clear and will leave a residue behind.

Now, due to the fact that my water clears quickly and doesn't leave a residue I'm sure it's just extra oxygen. But it has me wondering, because I'm paranoid and like to make sure, how harmful is calcium to axolotls? If it's harmful at all? (My rule of thumb is assume EVERYTHING is harmful to axolotls until told otherwise).

Calcium is not harmful to axolotls. They prefer their water to be hard, and many people add a little calcium in the form of crushed shells or coral to make their water harder.

Awesome, thanks! Now I don't have to worry.

Excess air in the water clears from the bottom up, as an extra check.