Making sure I understand the relationship of calcium, magnesium and alk

[athompson]

Without trying to get too technical, I am curious to see if I am grasping this concept. Calcium and alkalinity pretty much go hand in hand, with magnesium also playing a large role. So in concept, if one's calcium is at 460-480, but alkalinity is only at 7.2, and the magnesium is known to be low (1050-1100), would dosing the magnesium increase the alkalinity, or should one dose with say baking soda or an alkalinity buffer ( I have reef code B, but not A as I understood that to be the calcium part of the system and I obviously don't need more calcium).

I realize I am most likely jumping the gun. I am talking about my 10 gallon nano that is in day 7 of cycling with live rock and live sand. All signs point to my tank being cycled (had a 2 day spike of ammonia at .25 on day 4 and 5, but also had nitrates at 5~10 show up at the same time, never any nitrites. On day 6 and 7 amm and nitrites are zero, nitrates are ~5). I hope I'm giving enough detail without drowning anyone in my tank details AGAIN lol.

[downbeach]

Here's a good read:

http://reefkeeping.com/issues/2006-06/rhf/index.php

[disc1]

You can't change the level of one by dosing another. So no, you will never raise alkalinity by dosing magnesium. Where the relationship comes in is what numbers you'll be able to maintain. There is a limit to how much calcium and alkalinity you can have in the water together before they precipitate. It's called a solubility product. If you multiply calcium times alkalinity then there is a maximum on that number. Try to go over it and you'll precipitate calcium carbonate (equal parts calcium and alkalinity) until you get back below that number.

Magnesium comes in to help raise that number. How much depends on a multitude of things like temperature and pH. Magnesium interferes with the formation of calcium carbonate. So the more magnesium you put in, the more calcium and alkalinity you can put in. But you still have to put it there, it doesn't just magically appear.

[athompson]

Magnesium comes in to help raise that number. How much depends on a multitude of things like temperature and pH. Magnesium interferes with the formation of calcium carbonate. So the more magnesium you put in, the more calcium and alkalinity you can put in. But you still have to put it there, it doesn't just magically appear.

THAT is exactly what I as trying to figure out. How the magnesium correlates. Now the rest of it has came together for me. Thank you!

[planedoc]

I'm not a expert on chemistry but I can tell you that the purpose of dosing chemicals to maintain balance is mostly done on larger tanks to save money by adding things to your water that corals are consuming. With a tank 40 gallons and under its usually more economical just to pick a good salt and do frequently water changes. You still need to test but as time goes by you will feel comfortable knowing that water changes are keeping everything in check. If you have a 100 gallon heavy Sps tank it will consume calcium that even 25% weekly water changes can not keep up with. That is where dosing and other things come in. With a smaller tank weekly water changes are all that is needed. With that said, Chemistry is very important to understanding what is going on with your tank and how to diagnose problems. I'm just warning you not to over do it and not to add things unless you are sure you need to. BRS has lots of great videos and there are lots of stickeys in these forums that explain everything about chemistry. Balance is key and in smaller systems a quality salt mixture will provide that.

[bertoni]

Even with small tanks, water changes often aren't enough to keep the alkalinity and calcium in order. My 29g systems consumed 2-3 dKH per day, which isn't practical to replace with water changes.

I don't know what you mean by "maintain balance". There's really no such concept here.

[athompson]

I did a lot of reading but sometimes i just drowned in all the words ( a lot of the chemistry articles are very wordy) and get tired of reading before i find my answer.

[sleepydoc]

I don't know what you mean by "maintain balance". There's really no such concept here.

I'd have to disagree - there has to be some balance in terms of the rate of Ca/Alk/Mg consumption by organisms and addition to the system.

Regardless, my simple-minded explanation is that the Mg makes Ca and Alk more stable and keeps them from precipitating out. I've read (and understood) Randy's article, but so far, my simple explanation works for me! :spin3::spin2:

[jerpa]

I'd have to disagree - there has to be some balance in terms of the rate of Ca/Alk/Mg consumption by organisms and addition to the system.

Regardless, my simple-minded explanation is that the Mg makes Ca and Alk more stable and keeps them from precipitating out. I've read (and understood) Randy's article, but so far, my simple explanation works for me! :spin3::spin2:

There is a ratio for consumption. For every 1dKh of alkalinity consumed about 7ppm of calcium will be consumed and 1ppm magnesium although that varies based on what is doing the consuming. Coralline algae incorporates more magnesium than most corals and can skew that ratio a little.

With respect to the absolute levels in your tank there isn't really a balance. You need enough magnesium to maintain the other two in solution. If the magnesium is high enough then levels towards the lower end of the normal ranges are just as balanced as if the values are at the higher end. You will often hear people state that the absolute values must be balanced. Magnesium should be 3 times your calcium level and that the alkalinity level you target should corellate to your calcium as well to maintain a "balance". I believe this is the mythical balance bertoni was referring to.

[bertoni]

I'd have to disagree - there has to be some balance in terms of the rate of Ca/Alk/Mg consumption by organisms and addition to the system.
Do you have any evidence for this statement?