Magnesium

[hammondegge]

What is the relationship between PH, Alk, Calc, and Magnesium :blink and does an elevated Magnesium contentration (1500) have any ill effects?

[NaCl_H2O]

Jeez, Gary's gonna be all over this one, will probably wear out a keyboard on this one alone!!

FWIW - My Mg has always been 1500+ (or I don't know how to use the Salifert Mg kit :unsure). As I understand it, a Mg between 1300-1500 is needed to allow the needed suspension of Ca. Also, a high Alk tends to prohibit a high Ca concentration (I think that's right?). PH is a mystery to me, I drip Kalk and keep it at about 8.2-8.3

Here is a good link on the Ca/Alk relationship:

http://www.advancedaquarist.com/issues/nov2002/chem.htm

[NaCl_H2O]

Not meaning to push this off topic ... this is related ... and thus why PH is a mystery to me!

I always had somewhat low PH 7.8 - 8.0 until I started dripping Kalk, then I got it to lock in around 8.2. I have always had a fuge with lots of macro, and a DSB, and a Ca Reactor. My Kalk reactor has been off-line (Repairs needed) for about 3 weeks, but my PH remains at 8.2 :unsure

Can somebody 'splain that one to me?

[hammondegge]

Ooooops, sorry. (thanks steve) Let me reword that

What effect does magnesium specifically have on PH, Alk, Calc, (no need for Alk/Calc dissertation) and does an elevated Magnesium contentration (1500) have any ill effects?

Whew! :cry

[hammondegge]

Not meaning to push this off topic ... this is related ... and thus why PH is a mystery to me!

I always had somewhat low PH 7.8 - 8.0 until I started dripping Kalk, then I got it to lock in around 8.2. I have always had a fuge with lots of macro, and a DSB, and a Ca Reactor. My Kalk reactor has been off-line (Repairs needed) for about 3 weeks, but my PH remains at 8.2 :unsure


not off topic at all. i actually am interested to know more because i had ph dropping to 7.8 at night to 8.1 daytime and wanted to elevate this a point or two. the b-ionic just would not get there, so i started to dose magnesium to see if i could help it along. so far it hasnt made much difference, but i do have a magnesium level of 1500ppm now.

Calc is 380 and Alk is 9.0, PH is 7.88 this AM (a little better)

[matt]

Not meaning to push this off topic ... this is related ... and thus why PH is a mystery to me!

I always had somewhat low PH 7.8 - 8.0 until I started dripping Kalk, then I got it to lock in around 8.2. I have always had a fuge with lots of macro, and a DSB, and a Ca Reactor. My Kalk reactor has been off-line (Repairs needed) for about 3 weeks, but my PH remains at 8.2 :unsure

Can somebody 'splain that one to me?

It might have something to do with your Ca reactor. I found with my Ca reactor that I had to adjust it in a way that was not really intuitive; if the reactor ph was not low enough, the tank ph would tend to drop. Once I got the reactor ph and effluent flow really set right, my tank ph went up, from 7.8-8.0 (morning/evening) to 8.0-8.2. For me, the best adjustment was with a reactor ph of 6.6-6.7, with a nice slow effluent drip, and most important, effluent dkh over 30. The high effluent dkh allows you to drip less effluent from the Ca reactor and keeps the tank dkh pretty high.

If you're asking why your ph has not dropped 3 weeks after your kalkreactor was removed, my only guess is that it's possible the KW you dripped over time corrected any problem you might have had with too much dissolved CO2 from the Ca reactor....this is just a guess. If your ph starts to drop again, it's probably an indication that you should adjsut your Ca reactor.

Not that 7.8-8.0 is a problem in itself; lots of tanks using reactors run a little low on ph. If you have lots and lots of corals, it's likely that at night you have a lot of CO2 production from them.

[GaryP]

Let's see if I can do this without wearing out a keyboard.

Magnesium acts as an inhibitor to calcium carbonate precipitation. Magnesium loosely binds with carbonate and makes it unavailable to calcium to react with. This, in effect, provides a reservoir of carbonate and allows you to push your alkalinity and calcium concentrations higher without causing precipitation. Magnesium carbonate is much more soluble then calcium carbonate. As the carbonate concentration (alkalinity) drops, the carbonate ion is freed up from the magnesium complex and is made available to do the things that it does such as buffering pH and feeding coral growth.

How was that?

OK, now Richard's explanation. Calcium and alkalinity are like two different colored jelly beans in a jar. You can have so many of both color in the jar. When the jar overflows, you get precipitation. By keeping the magnesium level higher, you are basically increasing the size of the jar and allowing for more jelly beans to be added without causing precipitation.

Take your pick as to which explanation you prefer.

[hammondegge]

Perfect! they are both excellent. thank you Gary :)

[GaryP]

Your welcome. Do I need to address pH, or was that part already answered?

[GaryP]

Oh what the heck! Why stop when I am on a roll and I wouldn't want to disappoint NaCl_H2O! :) I'm going to start letting bstreep answer these questions. He knows this stuff as well, or better then I do.

Buffer (alkalinity) is like a bungee cord. It resists changes in pH, either up or down. A buffer consists of at least two components, usually a weak acid and a weak base. In our case those are carbonate (base) and bicarbonate (acid). Most people do not think of bicarbonate as an acid, but it is acidic in comparison to carbonate. Bicarbonate by itself has a pH of around 7.0 (neutral) and carbonate by itself has a pH of around 10 (alkaline). Remember that pH is a logarithmic scale. When you go from a pH of 7.5 to 8.5, the actual concentration changes by a factor of 10X. That why fish can be so sensitive to relatively small changes in pH if they occur rapidly.

There is actually a third component to this buffer. That is carbonic acid. Carbonic acid forms when carbon dioxide gas is dissolved in water. Hydrogen atoms switch back and forth between these three components of the buffer.

The actual pH of the water is the result of the relative concentration of these three components. There are a couple of other minor components such as acetate and borate but I won't drag those into this discussion now. The more carbonic acid you have, such as when there is an excess coming from a calcium reactor or when plants are generating it at night, the lower the pH. The more carbonate you have, the higher the pH. Bicarbonate sort of sits in the middle between the two others and acts to either accept or give up hydrogen atoms to maintain a balance and resist change.

When you buy buffer at the LFS it is actually a blend of carbonate and bicarbonate. Kalk neutralizes carbonic acid to form carbonate.

By the way, this is exactly the same system that regulates pH in your blood. If you have an excess of CO2 in your blood, such as when you're exercising heavily, your blood's pH may drop some (acidosis). When you are hyperventilating your blood's pH may increase some (alkadosis). The comparison to the aquarium is that by having good gas exchange, such as good air flow across the surface and an effective skimmer, its the equivalent of hyperventilating and helps maintain a higher pH in the tank. This is also why many people run a refugium on a reverse lighting cycle. The plants photosynthesizing when the main display lights are off use CO2 and help level out the dip in pH that is common at night. This is also why some people drip Kalk at night. It has the same effect, decreasing the amount of CO2 to prevent a dip in pH at night.

We think of plants as only making oxygen as a result of photosynthesis. They do that, but they also produce CO2 as a result of respiration. When they are photosynthesizing whent he lights are on, the net result is a decrease in CO2. When the lights are off, no O2 is being produced and only CO2 is being produced.

The natural pH trend in an aquarium is downward. That is because buffer is constantly being depleted by plants, corals, and neutralization by acids being produced by bacteria. Bacteria produce low molecular weight acids such as acetic acid (vinegar) and formic acid (ant venom). The buffer acts on these and the net result is less carbonate and more bicarbonate being formed resulting in a downward movement in pH. If the buffer wasn't there in the first place this downward change in pH would occur much more rapidly.

Does that help? Class is dismissed.

[hammondegge]

:w00t
cant help it can you? that too was excellent! thanks again.
robert

[hammondegge]

so can there be too much magnesium?

[GaryP]

Not really. I suppose there is some point at which Mag could be toxic but don't think you are ever likely to get there. Mag is a "light metal" as opposed to the heavy metal such as lead, mercury, silver, barium, cadmium, selenium, arsenic & chromium which are typically thought of as being toxic. That said, everything is toxic at some point. You can die from drinking to much water. Oxygen can be toxic at high levels.

Ever heard of "nitrogen narcosis?" Its a problem that divers have because of nitrogen at high pressure which results in a toxic effect. Yes, that's the same nitrogen that makes up something like 78% of the air we breath.

[Ping]

Thanks Gary. Your post's helped me fully comprehend Farleys older and last months article on making my own 3 part additives. It clears up the why it works.

[GaryP]

Your welcome. That's why we are here. I'm sure Farley did a better job of explaining it then I did, but you would have to go back and read a couple years worth of his articles to get it all figured out. Believe it or not, you got the Readers Digest version from me.