Using plain salt to reduce major elements

[Lenny_S]

Back in January while I was out of the country, I had someone taking care of my reef tank. During that time they overdosed Mg to the tune of raising it to 1600 ppm. Not awful, but not desirable either. Well after all this time and a lot of water changes and using pure calcium chloride instead of the 2 part (which has Mg in it) it is back down to a normal range.
But this brought an idea to mind for the future. I previously used IO Reef Crystals and RO/DI water to make up my saltwater mix. But that is already very high in Mg, Ca, and Alk, so since January I switched to the plain IO Salt Mix because it is lower in those things. That helped more, but it still took a lot of fairly large water changes.
What I just recently considered (with pool season coming up) is what if I used plain old NaCl? I looked up Morton's pool salt mix, for example, and the MSDS said it was 100% NaCl with only trace amounts of Magnesium and Calcium salts.
In the example of reducing Mg levels, would using a salt like this and simply adding my own calcium, carbonate alkalinity, and trace elements (leaving out any Mg) be a viable option to reduce Mg more effectively?
My thought is I could do much smaller water changes with that kind of mixture to get the same or better reduction of something like that as compared to virtually any of the aquarium salt mixes. Starting with basically pure NaCl, you could apply this to just about anything, high Ca, Alk, Boron, I2, K, whatever... just leave out the item you are too high with and you can get better reduction without a series of much larger water changes.
Anyone else have a thought on this?

 

[Randy Holmes-Farley Verified Community Expert]

That would work, but you'd basically be making a salt mix with low levels of one or more specific ingredients, which seems a substantial bother.

 

[JimWelsh]

I did a very similar thing recently. My Triton test showed my tank had elevated levels of boron, strontium, potassium and bromide, plus extremely elevated lithium. About a month ago, I did prune a bunch of overgrown corals, and shipped some of the larger ones off to a friend. While I've been running without water changes for quite a while, this necessitated about a 10% water change. I took advantage of this opportunity to make up my own salt mix using NaCl (swimming pool stuff), CaCl2, MgCl2, and MgSO4 only, which I used for that water change. I haven't seen any noticeable adverse effects. I haven't sent a sample to Triton after this, but intend to do so soon.

 

[Lenny_S]

Thanks for the replies. I'm seriously considering DIY salt mix. This experience with the Mg has also made me more aware of what a lot of companies add to their 2 part. My calcium (part 1), for example, has what the company considers to be appropriate amounts of Mg, Sr, and whatever else. That's all well and good, but then you are simultaneously doing WCs with a salt mix that is adding whatever they consider to be appropriate and from what I've see, at levels elevated from what I keep mine at.... then I just personally feel like I'm fighting it and need an advanced degree in chemistry like Randy to be able to have more predictability and stability.
I think for small, frequent water changes, it can be worked out by just adjusting whatever other dosing you may be doing, small WCs are probably negligible. But normally I'm doing larger less frequent water changes. And if you are trying to correct a mistake or accident, it's a lot more work and a lot slower with salt mixes (IMHO).
It's good to know that DYI salt mix is a viable option. By the way, @JimWelsh what swimming pool salt brand did you use?

 

[JimWelsh]

The brand I am using is "Pro's Pick" Professional Grade Pool Salt.

If you're going to do this, you need to make sure that you understand how to calculate the correct amount of the hydrated salts (CaCl2*2H2O, MgCl2*6H2O, and MgSO4*7H2O) to use, and how to also correctly balance the Cl- and SO4--. Many people are confused by these things. I would also strive to make sure your MgCl2 source is as pure as possible, since it can be a source of a number of undesirable contaminants, most notably ammonia. In my case, I'm pretty sure my extremely high lithium came from the brand of MgCl2 I used to use. I am now using USP grade.