No idea what the hydration is, just says MgCl on bag. Not sure the data sheet indicated either. Just regular old ice melt. I don't want to dig into the depths of my brain and calculate molecular bonds :)

Bah, don't worry about the hydrate
I just looked into it. All it means is how much water it contains

I'd say go with your 3 cups of 10:1 for a start
Of course, you'll want to boost your current level as I recall you said it's lowish

10:1 MgCl2 (SafeStep) to MgS04 (Epsom salts) dumped into my water change container. Been doing that since late last fall.

So, you finally decided to start adding Mg....

Same amount as Russell?

And ya, thought I'd play with it, see if it matters.

Yup, Russell put me onto Randy's formula, and no reason to try anything different. I initially had to raise my Mg a bit in my tank so was using 500ml MgCl2 for a couple of water changes. But now, 250ml seems to be enough. This is for a 230g system.

Great, thanks. I get mine on Friday, so next water change will get some Mg

Neh.. just shake your bucket of IO. You will get all the mg that you need.

10:1 mix or 7.25:0.75 mix for people running calcium reactor.

I use brightwell neomag(domolite) in the reactor. but since I am too weak/lazy to shake or turn my bucket of IO. I add mg mix into the nsw.

That's where the problem is. I don't buy buckets, I buy the box. I try to drive really crazy bringing it home, but Mg is still low (I think)

I can get bulk chemicals (buddy owns a chemical company) including Alk (Soda ash), Calcium chloride and mag. Mag Chloride is expensive at roughly $220 per 50 lb bag, but Mag sulfate was cheap at roughly $60 per 50lb bag.

It looks like TimT is the better solution then for Mag Chloride as it would only cost 86ish for a 50lb bag. I wonder if one is pharmaceutical grade which might explain the difference.