Dom, I hear that all the time, which is what makes me wonder why. I never dosed Mg (because there was none) and never had a problem. It's just one of those things that confuses me. I tried to believe, and added Mg, no difference in my tank. But really, for the cost of Mg, I don't see anything wrong with "just in case" application :)

P.S. Figured the OP got his answer already :)

Brad, did you notice any difference in the amount of calcium and alkalinity you had to add after raising magnesium? What do you run them at?

Again, it's not necessarily that it's a problem to have your mag a little low, just that it can be a little harder to maintain levels of other elements. Whether or not this has a noticeable effect in your tank will depend on a variety of other factors... I'm sure many people won't notice a difference.

my numbers have always been around 420/8dKh. This is with reactor or with kalk. Since I've never used a doser, I cant say that I used 4ml extra Ca with/without. But again, if I did, do I want to save 4ml Ca by using 20ml Mg (numbers made up, no idea what people use).

I can't/won't offer an opinion saying you need or don't, I just find it odd that so many tanks did so well for all the years before Mg came along. Maybe more do better now? I was kind of disappointed that after starting to use it, I didn't see any change in anything. I guess I was hoping for magical growth or something. But for the cost of the ice melt I'm using, I figure I'll just keep adding, mostly because Randy knows more chem than I do :)

Ya see, I couldn't get my Ca above 380ish until I boosted my Mg

Welcome to the dark side David :smile:

I would suggest the same as Bblinks did. Having your mag in that range makes it much easier to balance the other 2 while using less. Lower mag levels will give you a seesaw effect when adding the other 2 making stability difficult.

Many of us use IO Sea Salt. It's pretty normal for it to be high Alk, slightly low Ca and lowish Mag.

I dose mag and then ca to my new water before adding it to my tank. Some dose it after adding, and some don't bother at all. So it's up to you where you want your tank parameters to be.

As for what products to use there's the expensive, easy to use liquids and there's the inexpensive powders. Any one you choose is fine.
For now I'm using bulk powders and following Randy's 2-part. If I had the money I'd get a Calcium Reactor and dose mag accordingly.

If you haven't moved in the last 3 years you should walk over sometime for a chat and check out my system

Thanks everyone for getting into the topic. Like many mention here Mg need to be in check before adding cal or alk as I also notice I add lots of A and B dose and calcium liquid as well but still couldn't get Cal to increase pass 370 from 340ppm. Alk in other hand I see it increase so let me get Mg in range and dose cal after see if I can bring it up to 420ppm.

Hi Greg, good to see you here as well. No I haven't move anywhere yet just more busy with life only. I am still in debate of getting a doser or the calcium reactor for my 180G. I have no problem dosing it just need to get something that cost effective and easy to maintains and more time to enjoy the tank. Don't want to turn it into a part time job just to keep up with the tank. Maybe my next topic would be reactor or doser for 180G tank?

I think you just answered the debate
A reactor is much less work as far as I understand

No question in my mind. For a 180 with any amount of SPS, Ca reactor is the way to go. I regret I didn't do it sooner.

typical ocean water is Ca-420, Alk-7 and Mg only 1280, personal experience easier to bring the Ca up if Mg isn't low.