Let's talk about Alkalinity, Calcium and Magnesium in an SPS Tank

[dheinze]

hmm...I do about 10% wc weekly; I guess I thought this would've caught up with the alk situation sooner than it has (a couple months and running here). Maybe I will do an alk test on my freshly made up seawater (I use seachem reef salt), and see where that is.

[melev]

This thread has been nominated for Thread of the Month. You can vote for it in this poll:
http://reefcentral.com/forums/showth...readid=1193958

[KurtsReef]

I have only recently started too keep SPS and feel as though I need to relearn all the chemistry aspects of reef keeping again. Coming from the much simpler world of soft corals, my routine simply did not include testing for many things and my system ran quite well...

Now with a larger system, attempting too keep more difficult items such as SPS I have been re-reading and reading articles/books getting back up to speed and had forgotten how complex this can be.

Tested Mg for the first time yesterday and it came in at 1050ppm so will be trying to raise that too the 1300 mark in the next few days using Bionic's Mg suppliment.

I have been using the Bionic two part since before beginning the larger reef system, but now own a calcium reactor I just need to set up and dial in. Plan on still using the two part in addition too that as the Ca reactor is more than likely not large enough.

There was mention of Mg (low Mg) in a system effecting the color of your SPS...I am very new too SPS, however noticed after picking up a frag of staghorn coral from a LFS which appeared too be very brown in the store that after being in my system for a couple of weeks it now has very purple tips and a more light color too its main body...not sure what caused the welcome color change however want too keep that kind of success going as well as obtain good growth. I only have 4 frags of SPS right now and all seem too be doing well.

[Aquarist007]

Originally posted by melev
This thread has been nominated for Thread of the Month. You can vote for it in this poll:
http://reefcentral.com/forums/showth...readid=1193958

I am torn between this and the misconceptions thread--how many votes do we have?

[five.five-six]

Originally posted by MJAnderson

I can't find it now, but one of Randy's articles talked about what you can dose in kalk. I THINK one of them was Strontium.

well it appears to be fairly common practice to add iodine to Kalk, from what I understand strontium is not all that critical for a successful tank... I do not even test for it. should I?

as for the thoughts of your anemone, they are like women, no one understands why they do what they do.. if it can find just the right light and flow, and especially if it can get it's entire foot inside a hole, it may stay put for several years and then just get up and sting your favorite frag

[Aquarist007]

Originally posted by five.five-six
well it appears to be fairly common practice to add iodine to Kalk, from what I understand strontium is not all that critical for a successful tank... I do not even test for it. should I?

as for the thoughts of your anemone, they are like women, no one understands why they do what they do.. if it can find just the right light and flow, and especially if it can get it's entire foot inside a hole, it may stay put for several years and then just get up and sting your favorite frag

IMO dosing with either of them is not necessary if you are doing routine water changes.

I am not commenting on the other thought about the anenome----my wife reads these posts from time to time.

[chessmanmark]

This post is getting lost now. 11 pages back to find it today. Any chance of making this one a sticky JB?

[JB NY]

Like that?

[JetCat USA]

Good threads don't need stickied

[chessmanmark]

Thanks, now I don't have to work so hard searching for it. Good info, such as that delivered in this thread, should be readily available.

[cutegecko3]

ive tried running high alk. and lost bright colored tips on my acros. so i keep mine at natural seawater level,and calcium at least 400.never tested for mg. im just learing what role that plays.

[gary faulkner]

OK to talk about types of media for reactor?

I need to order some and was using ARM. It seems to turn to mush too easily. Wondered if I should try some larger media?

Hope this isn't a hijack!

[JetCat USA]

the small grain ARM will only turn to mush if the reactor pH is driven to low either by operator error or the recirculation flow becoming restricted. correcting that problem will prevent the mudding, going to the larger media will help with any recirculation problems but will also mud if the low pH is operator error. and to keep on track, once mudded the media regardless of name brand will not supply Ca/Alk to the system. on a side note, ARM IME is the best at keeping Sr levels in check.

[MCsaxmaster]

Just a couple of comments on magnesium as I'm not sure these questions were completely addressed (appologies if I missed it).

Magnesium is important in a conversation like this because it forms ion pairs with carbonate in sea water (and bicarbonate). Calcium carbonate is substantially supersaturated in sea water (on the order of 300 - 400% typically) and we can easily raise that to 600%+ by maintaining higher alkalinity in captivity. We'd predict that calcium carbonate should spontaneously precipitate, since there's way more of it dissolved in the water than there "should" be. However, that's not what happens. One of the reasons is that magnesium forms those ion pairs with carbonate, making it more difficult for calcium carbonate (solid) to form and precipitate. In addition, magnesium carbonate tends to precipitate out with calcium carbonte during abiotic precipitation. Magnesium carbonate doesn't fit into the crystalline structure of calcium carbonate (whether that is CaCO3 as aragonite, calcite, or even amorphous CaCO3). That tends to discourage further precipitation. So, magnesium really gets in the way of calcium carbonate precipitation and allows CaCO3 to remain supersaturated.

Magnesium is extremly abundant in sea water. Yes, Mg is an imporant nutrient for any cell, but cells use so little Mg in their normal biology that it is essentially a drop in the ocean. Magnesium does also precipitate with calcium carbonate though, and calcifying organisms like corals, coralline algae, etc. consume it (just like they consume calcium). However, corals, which produce aragonite, consume Mg very, very slowly. Corals consume about 19 moles Ca for every 1 mol Mg. Magnesium is also about 3 times as concentrated as calcium in normal sea water. Thus, the Mg is 3X the conc. of Ca and gets used by corals at ~1/19th the rate. Very modest replenishment of Mg will easily replace what is lost to coral calcification.

On the other hand, coralline algae produce high magnesium calcite. This is a structurally different form of calcium/magnesium carbonate as compared to aragonite, it is more soluble, and has much more Mg. Typically coralline algae have Ca:Mg stoichiometry in the neighborhood of 4:1, not 19:1 as with corals. Coralline algae consume Mg proportionally much faster than corals, though coralline algae also tend to calcify a lot slower than corals. A lot of coralline algae growth can consume a fair amount of Mg, however.

Some salts do tend to be deficient in Mg as well, leading to problems from the get-go.

Recent evidence suggests that strontium is probably incorporated into the skeletons of calicifying organisms (as is lead, uranium, cadmium, etc.) simply as an impurity. The organisms are not necessarily going to any effert to put these into the skeletons--they end up there just because they get precipitated along with everything else. Magnesium, no the other hand, has very particular distribution patterns in coral skeletons, so it looks like the corals might really be "doing" something with the Mg, though nobody has a clue what that something might be.

Chris

[MCsaxmaster]

Also, just a note on alkalinity:

There are two definitions you'll typically run into for what total alkalintiy is. One tends to be preferred by oceanographers while the other tends to be preferred by analytical chemists (and both get used by chemical oceanographers ). The two are not mutually exclusive, but two different perspectives of the same property.

The oceanographic definition, which is not really useful to aquarists, is as follows (my wording)

Total alkalinity: the difference in concentration (molar or molal) between strong cations (+ ions) and strong anions (- ions) in sea water. Here "strong" means strong electrolytes (i.e., they completely dissociate).

While this is most certainly an appropriate definition, it isn't conceptually very useful for us.

A definition used by analytical chemists is more useful to us:

Total alkalinity: the excess concentration of proton acceptors over proton donors in sea water, determined when a sample is titrated to the carbonic acid endpoint. Expressed as the equivalent concentration of HCl necessary to reach the endpoint.

So, the total alkalinity is the concentration of everything that will buffer against a drop in pH (bicarbonate, carbonate, borate, phosphates, etc.) minus everything that will buffer against a rise in pH (free H+, HSO4-, etc.). The total alkalinity is the concentration of H+ that all the little bases can neutralize.

In sea water ~96% of the alkalinity is provided by the carbonate system, that is, by bicarbonate and carbonate ions. Of this 96% about 88% of the buffering is due to bicarbonate and about 12% is due to carbonate. Of the 4% of total alkalinity that is not provided by the carbonate system, most of it is provided by borate (~4%). Ions like phosphates, silicate, etc. also provide alkalinity, but they are usually so low in concentration compared to everything else that they don't make much of a difference in the context we're talking about (very important in porewater in sediments, or near hydrothermal vents, for example).

Corals and other calcifying organisms build skeletons out of some form of calcium carbonate. Since most of the alkalinity in sea water is provided by the carboante system (96%) we use total alkalinity as an indicator for how much bicarbonate and carbonate there is. Most critters probably use bicarbonate and transform it to carbonate at the site of calcification, but that step is unimportant here. This is why we want to always make sure that we use alkalinity supplements based on bicarbonate/carbonate and not something like borate. Borate will provide alkalinity, but not alkalinity that is useful to calcifying organisms.

Chris

[JB NY]

Good stuff Chris. Thanks for that contribution.

[Aquarist007]

I like your writing style--chris--technical but not too technical--start working on a book if you haven't already.
Scott

[Aquarist007]

I have read or been told that under certain conditions--low calcium high magnesium that corals will use magnesium and combine with the carbonates---to calcify ???

[Aquarist007]

Is kent super DKH---a non borate ph/alkalinity booster? If not what would you recommend--other then dosing with Kalk

[MCsaxmaster]

Good stuff Chris. Thanks for that contribution.

No worries

I like your writing style--chris--technical but not too technical--start working on a book if you haven't already.

Ha, thanks! I'll get things written in a larger format someday. For now life is just too busy to do much more than magazine articles/reef club presentations.

I have read or been told that under certain conditions--low calcium high magnesium that corals will use magnesium and combine with the carbonates---to calcify ???

They always use Mg when they calcify, just not very much (very, very small portion of what is available). I suppose it is possible that they might increase use of Mg when Ca is low, but given recent findings I'd be skeptical of this. Of course, ya never know until you try it, and I don't believe anyone has ever done that.

Is kent super DKH---a non borate ph/alkalinity booster? If not what would you recommend--other then dosing with Kalk

That should be fine to use. It is most likely just a mix of sodium bicarbonate with a little sodium carbonate. Seachem's buffer (I forget the name) has a lot of borate in it, which can lead to problems. Honestly, considering how cheap sodium bicarbonate is relative to most salts, I don't know why any company would rely on borate alkalinity, but anyway....

If you need to boost just alkalinity I'd use either baking soda (sodium bicarbonate) or baked baking soda (sodium carbonate) as per Randy Holmes-Farley's articles on the subject. It's extremely cheap, and does exactly the job we want. Since it's intended for human consumption, it's probably as pure as any product we could buy (though not as pure as like reagent or analytical grade sodium bicarbonate intended for lab use).

cj

[sdoggssf]

Hey everybody, Sorry if this question has already been asked but i was wondering how to lower DKH? My DKH is around 16.0 and my CA is at 420, fortunatly all my corals have great color. However, with my DKH being so high i know there has to be some improvement if it is lowered. Does anyone have any advice?

[melev]

First thing I would do is get someone with some test kits to verify that those results are accurate.

If they are truly that high, stop dosing anything (two part buffers, kalkwasser, calcium reactor) for now, and do a 25% water change.

[Aquarist007]

Originally posted by sdoggssf
Hey everybody, Sorry if this question has already been asked but i was wondering how to lower DKH? My DKH is around 16.0 and my CA is at 420, fortunatly all my corals have great color. However, with my DKH being so high i know there has to be some improvement if it is lowered. Does anyone have any advice?

running high alk level you take the chance of some rapid precipitation of carbonates and or rapid corraline algae growth.
Either way that will consume carbonates and indirectly affect coral growth

[Aquarist007]

------I agree with melev----20- 25 per cent water change and bring it down to around 10.5 dKH

[JB NY]

Easiest way to bring your alk down is to only dose calcium for a while. Just check your alk every few days, you will notice that the alk seems to drop more than the Ca. Meaning, you might notice your alk drop 1-2 points before you see you calcium drop much at all. just dose some turbo calcium or some other calcium only additive (to keep the calcium levels stable) until the alk is where you want it, then re-start your normal dosing routine.