You pick the change poll

[Delphinus]

Not sure about either one to be honest.

Thoughts on Mg: IME, Mg technically isn't a problem unless it's very low. I do actively dose Mg I suppose you could call it, but I do it via my water changes: I add just enough MgCl and MgSO4 to my new water to bring it up to around 1500. That tends to keep the Mg in the tank at "good enough" levels. So I don't think "worry" about Mg. It's just a routine.

I don't understand the science behind it, but I've noticed that things just look better when Mg is at "good enough" levels (versus "far too low"). The change is most noticeable in anemones (of which I have a handful). Ever since adopting the water change technique however I haven't noticed them looking off due to Mg levels in probably 4-5 years now or more.

Guess the thing to try is seeing if your Mg is low, then dosing it back to seawater type levels, then see if you notice a difference in your tank.

Thoughts on carbon: I used to think that reactors were a better choice for carbon as I thought water passing through the column of carbon would make for better absorption of the baddies because of better contact to more surface area blah blah blah something or other. But seem to have read more than a few credible articles in the last few years that seem to suggest just having a bag in a high flow area in the sump is good enough because osmosis or something blah blah blah the main take away is it still works as carbon.

I made the investment in TLF reactors so I figure I might as well use them for carbon but if I didn't have them already I'm not sure I'd worry about it too much.

Guess the thing to try is move your carbon into a reactor and see if you notice a difference in your tank.

[Aquattro]

Originally Posted by Delphinus

Thoughts on Mg: IME, Mg technically isn't a problem unless it's very low.

Let's expand on this. What is "very low" and what would the problem be? Mine is about 1150ppm and I don't really see any problems. Looks like a lot of work to chase a number without understanding the problem.

[kien]

Originally Posted by Aquattro

Let's expand on this. What is "very low" and what would the problem be? Mine is about 1150ppm and I don't really see any problems. Looks like a lot of work to chase a number without understanding the problem.

In my experience, a result of low mag is that it makes it more difficult or challenging to maintain higher alkalinity levels. There's a whole chemistry lesson you can read up on regarding the relationships but what I took away was simply, low mag will bugger up alkalinity. To me low is below 1200 is when things start to get interesting.

[Aquattro]

Originally Posted by kien

To me low is below 1200 is when things start to get interesting.

Hmm. Mine is (being generous) ~1170. I'll test alk, pretty sure I have a kit for that

[Aquattro]

Originally Posted by Aquattro

Hmm. Mine is (being generous) ~1170. I'll test alk, pretty sure I have a kit for that

Alk is 8dKh. Sounds good to me?

[kien]

Originally Posted by Aquattro

Alk is 8dKh. Sounds good to me?

If your Alk is fine and you're not finding it difficult then I personally would not worry about mag. I use Alk as my indicator for potential mag issues. My mag as been as low as 1100 and the only thing I noticed when I had it that low as that it was more challenging for me to maintain my Alk higher. It certainly wasn't the end of the world. I have never dosed mag and have only tested for it once in the past 3 years.

[sphelps]

Originally Posted by Aquattro

Let's expand on this. What is "very low" and what would the problem be? Mine is about 1150ppm and I don't really see any problems. Looks like a lot of work to chase a number without understanding the problem.

IME low mag = unstable Calcium & Alkalinity. Magnesium helps allow for supersaturation of calcium carbonate so the lower the mag the lower saturation level. My understanding is anything under 1200 ppm is low but then again if you're happy with your current Ca and Alk levels then Mag is likely fine at whatever it is even if lower than 1200ppm. However higher mag levels should result in higher efficiency from a Ca reactor and perhaps better growth as well, whether or not this would be noticeable though....

[Delphinus]

I'd consider 1150 to be in the "good enough" levels. I think basically 1000-1100 or above is sort of my own threshold. I think NSW sits around 1300. I haven't seen any adverse effects having it as high as 1400-1500. I haven't tested any higher because it takes a surprising amount of Mg to raise the levels at all so going any higher than that wasn't economical. I would imagine, however, that there is a point where it's too high and could cause problems .. I just haven't empirically tested for the limits.

When I did notice problems with low Mg, I found that Mg was somewhere around 600-700 and it was due to the salt I was using at the time. Not sure if I had a bad batch or a bad brand but it was one of those little life lessons where the takeaway was that you should test your incoming salt from time to time. (One more reason I choose to stick with IO these days: it's been the most consistent for readings out of any I've tried, and if the levels aren't exactly optimal, they are at least the same amount not exactly optimal from bucket to bucket and I like consistency more than I like paying more for salt that ends up being less consistent.. Oops I just turned your poll into a salt talk.)

In particular, when Mg starts to dip under 1000, I first notice that the anemones expand during the day less than they normally do. This I've noticed enough times (maybe 5 or 6?) that I'm convinced it's not a coincidence. And the lower the Mg drops from 1000, the smaller they get. Also, they start expanding again when I start raising the Mg in the tank (I never adjust more than 100 per day, just for the sake of keeping changes slow).

It is the strangest thing, I don't know why anemones care about Mg, but I'm convinced they do.

Not sure it counts as empirical evidence to back the claim, but there have been a few times people would ask "hey how come my anemones don't expand like they used to" on here, I'd usually chime and say "check your Mg, couldn't hurt" and I seem to recall most, if not all, came back and confirmed that they had low Mg levels. So I'm totally convinced there's a connection, even if intuitively I can't understand why an anemone cares about Mg.

[Delphinus]

As far as the relationship from Mg to Ca and Alk .. yeah, there's a bunch of fancy articles you can read but my main take away from all that is "it takes more Ca and Alk dosing to maintain more gooder levels of Ca and Alk when Mg is low."

So raising your Mg a wee bit (because I don't think I'd worry too much about 1150, although if it were my tank I'd bump up the Mg on the next water change) I'd expect that you might need to bump down your Alk and/or Ca dosing by a wee bit. That said, you might not need to because who knows maybe the uptake will increase thus keeping everything stable, except maybe stuff grows a tiny bit faster. (A bit of a stretch but who knows..)

[Delphinus]

Also from back when I did run a reactor for Ca and Alk, I found that Mg just worked out to where it needed to be.

I've been kind of thinking actually of putting a Ca reactor back online on my tank. When I look back I always had way better SPS growth on tanks with them than without them. I just don't cherish the thought of needing to refill CO2 tanks every few months (which for me was sort of the ultimate push away from a reactor in the first place). I wonder though, if one could just just keep the Ca and Alk dosing and have a small reactor as a kind of supplementary measure and then it's not as big a deal to take the reactor offline for a week to get a tank refilled or whatever.