corvettecris;227043 wrote: And thus, that is why IO is not recommended for a reef tank. It is designed to be fairly cheap, and low on minerals. It is perfect for fish only tanks, but if you want to reef, you will probably need to upgrade salts.
Funny, I have been using IO and supplementing the Calcium and alk with kalkwasser for water changes for about 15 years now with great success in stony reef husbandry, it has been one of the few salt mixes that has been consistent over the years... It's high in alk, one of the few areas I find a number of mixes to be deficient in, and the rest of the elements mix in at NSW values when mixed to S= 35 PPT. If your ASW is not at 35PPT ( SG=1.026@25<sup>o</sup>C), your Mg++ will be low by whatever percent of 35 PPT your salinity actually measures in at. for example, if you are running your salinity at 32PPT ( SG=1.0235-1.0240@25<sup>o</sup>C), then you should expect your Mg++ to measure at 10% below the Mg of NSW with a salinity of 35PPT, or a Mg = 1170 to 1200 PPM (mg/l) rather than 1300 PPM (actually it is 1290 PPM, but 1300 makes the math easy).
You can calculate molarity as well using SG if you want to do the math to check the values:
Molarity = Mole of Solute per 1 Liter of Solution
Mass = Volume x Density
Mass of 1 Liter of the Sea Water
= 1 Liter x ( 1000 ml / Liter ) x ( 1.026 g / ml )
= 1026 g
Mass of Magnesium ion in 1 Liter of Sea Water
= 1026 g x ( 1290 mg / 1 kg ) x ( 1 kg / 1000 g ) x ( 1g / 1000 mg )
= 1.323540 g ( in 1 Liter of Sea Water )
Number of Mole of Magnesium ion in 1 Liter of Sea Water
= 1.323540 g / ( 24.305 g / Mole )
= 0.054455661 Mole( in 1 Liter of Sea Water )
By Definition
Molarity of Magnesium ion = ~0.0544 M
Doing the same series of calcs for a SG of 1.0235 results in a molarity of
0.049010094 or ~0.0490M ( 10% less than 0.0544)
Remember that seawater displays a conservation of proportionality of the elements that make up its ionic composition, so that regardless of the salinity, the elements will always be in the same proportion to each other. Samples taken all over the world from different seas confirm this. See Millero's <u>
Chemical Oceanography</u> for more info on this tenet of seawater.
In our tanks, these closed systems often get off in proportionality of the conservative elements as a result of biological sinking of some elements, or in the case of Mg++, get skewed as a result of the injudicious use of two part hermatypic supplements. When we use calcium CHLORIDE and SODIUM bicarbonate to supplement the hermatypic needs of stony corals, they use up the calcium and the bicarbonate to make skeletons, leaving behind the sodium and the chloride. Over time, this unused salt becomes a major component of the salinity of the tank. As we adjust the salinity down to make up for this accumulation of NaCl, we remove the Mg++, K+, sulfate, and borate/boric acid, etc. (usually by taking a gallon of the old water out and adding a gallon of RO/DI to drop the salinity). Over time this changes our mix from ASW to a brine primarily made up of sodium and chloride ions, of which Mg++ becomes an insignificant part of the mix (and no longer supports supersaturation quotients so we can have relatively high calcium in the presence of bicarbonate/carbonate).
If your intent is to compare the Mg++ levels of one salt mix to another, make sure that you compare apples to apples, and make your sample have a S=35 PPT.
Just to check, I mixed up some IO here just now to 35 PPT salinity (refractometer based at 80F) and tested with a Salifert kit; it came out with 1320 Mg++/l. I gueses IF I wanted to belabor the point, I could run a series of 10 tests starting over each time to get an average, but this was good enough for me in view of the fact that this is around what I usually see. I certinly don't want to start a long discussion here over the merits of each salt, but I DO want to point out that unless you make each batch of salt to the same salinity, using the same method of preparing the salinity and the salinity test, that you'll get different values for each test you run, even comparing IO to IO.
HTH
