Is anyone dosing rolaids?

[trueblackpercula]

has anyone check the contents of rolaids it will shock you.
Here it is and can it be used for daily calcium and magnesium usage in the reef tank?
calcium carbonate 675 mg
magnesium hydroxide 135mg
Michael

[bertoni]

The magnesium hydroxide would dissolve. The calcium carbonate won't. So it won't add calcium or alkalinity to the tank.

[trueblackpercula]

O well just a try :)

[Boomer]

That magnesium hrdoxide will not dissovle either, it is not like calcium hyroxide. It needs a low pH. It is less soluble than Aragonite or Calcite

FW

Mg(OH)2 pKsp = 10.82
CaCO3 (Aragonite) pKsp = 8.2
CaCO3 (Calcite) pKsp = 8.3
Ca(OH )2 pKsp = 5.3

[DrBDC]

Same problem with those commercials. Is it tums or rolaids (tums I think) that advertise they have calcium which is good for you. Well they will neutrilize stomache pH so it's unusable (mostly). They didn't lie, they have calcium, and calcium is good for you. Now the orange juice with calcium added is good due to acidity or if you really wanted you could drink some vinegar with the tums! :D

[David Grigor]

<a href=showthread.php?s=&postid=8834605#post8834605 target=_blank>Originally posted</a> by DrBDC
if you really wanted you could drink some vinegar with the tums! :D

sounds tastey......

[bertoni]

I thought magnesium carbonate was insoluble, but magnesium hydroxide would dissolve.

[Boomer]

No Jon, it is practically insoluble in FW but it is not as insoluble in seawater. Of course most things are more soluble in SW as it has a higher ionic strength. That is why you don't see any posts on using it as an additive/sup. The lower a pKsp is the more soluble it is and the higher it is the less soluble it is. Magnesium carbonate is actually more soluble than Mg(OH)2 or even aragonite.

Here is a solubility link. Just look at the 10^ - x. The bigger the -x number is the less soluble it is.

Example: for Aragonite it is 10^-9 and Calcium hydroxide 10^-6. So, Aragonite is much less soluble than Calcium hydroxide or Calcium hydroxide is much more soluble than Aragonite.


For FW Tables ( these 10^-x numbers will be smaller for SW, meaning more soluble. In seawater Aragonite is about 8.9 x 10-7 vs FW 6.0×10-9, so it is more soluble in SW)

http://www.ktf-split.hr/periodni/en/abc/kpt.html

[Mike O'Brien]

When you add a high ph alkalinity suppliment to the tank it form's magnesium hydroxide. That is soluble in sea water because it dissolves pretty fast as the local ph lowers.

What's different with this magnesium hydroxide and why wouldn't it provide alkalinity from the hydroxide like the hydroxides ?

[Boomer]

I stand corrected to a degree and was relying to much on FW data. I did a search here and found an old thread. There is also the issue of the cloudy, a transient pecip vs a solid mass of the hydroxide. Usually, what we see is this cloudy which does go back into solution, as it is an unstalbe form, where solid blocks are another issue and are much more stable and less soluble.

http://reefcentral.com/forums/showthread.php?s=&threadid=144567


The issue of magnesium hydroxide is very complicate as seen by this thread. Randy also has a long say on it in this article again showing how complicate the issue it.

Taking this cloudy solution at pH 10.4, I added hydrochloric acid to reduce the pH to 10.0. All of the cloudiness disappeared within a few minutes. When set aside for 90 minutes, however, a solid precipitate formed. Upon reducing the pH to 8.2 with hydrochloric acid, this precipitate remained. It remained undissolved for many days.

http://www.reefkeeping.com/issues/2005-07/rhf/index.php


In order to substantiate the theoretical calculations described above for magnesium hydroxide, I also tested the precipitation of magnesium hydroxide at elevated pH. Starting with fresh Instant Ocean artificial seawater, I added dropwise a concentrated solution of sodium hydroxide in fresh water. As each drop entered, a cloudy/white glob formed that settled to the bottom. At first, each drop could be fully dissolved with sufficient swirling. By the time the pH of the solution reached the upper 9's, the glob was only very slowly dissolving. By pH 10.4, the solution was very cloudy, even after extensive swirling.

Taking this cloudy solution at pH 10.4, I added hydrochloric acid to reduce the pH to 10.0. All of the cloudiness disappeared within a few minutes. When set aside for 90 minutes, however, a solid precipitate formed. Upon reducing the pH to 8.2 with hydrochloric acid, this precipitate remained. It remained undissolved for many days.

My conclusion is that the initial cloudiness is magnesium hydroxide that rapidly forms and dissolves (not magnesium carbonate, as described below). It appears somewhat more soluble than the theoretical calculations above would suggest. That is, it does not precipitate out until the pH is above 10, and seems fully soluble at pH 10, while the calculations suggest that the initial point of precipitation should be lower (mid 9's). This result appears to be because the magnesium hydroxide that precipitates first is not the most stable form, and it is the most stable form (the crystalline form brucite) that is typically reported in Ksp values. The initial precipitate is faster to form, but is more soluble.

[IslandCrow]

I can still use Rolaids if my fish have indigestion, though, right?

[Boomer]

Mike I hope you do not fly that plane :lol: :D

[DrBDC]

<a href=showthread.php?s=&postid=8842467#post8842467 target=_blank>Originally posted</a> by IslandCrow
I can still use Rolaids if my fish have indigestion, though, right?

It might work on seahorses, they get that gas bubble disease. :D

[IslandCrow]

Believe me, even that plane isn't as complicated as this hobby can be at times.