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

[JB NY]

Ok so let's start a new discussion. This time I think it would be a great idea to get some of the basics down. So the topic will be Alkalinity, Calcium and Magnesium. Please note if you are going to participate in this discussion. Please stay on topic. This is not the place to ask where to buy something or just to pop in a state what you use. If you are going to post here please try to add something constructive. I am all for people agreeing with a members comments and such, but if there are posts that seem to be taking away from the discussion, they will simply be removed from the thread. OK back to the topic.

I choose these three to discuss together, because getting the correct numbers on each is essential for maintaining all.

I am going to give a run down on how I choose to remember and use each of these elements for my tank. Others feel free to comment and add on to what I have written. I am not a chemist and never claim to know half of what is needed to be a chemist, so with that disclaimer out of the way, here we go.

Alkalinity.
Trying to actually read on what Alkalinity is will most likely give the average reader a headache to say the least. It seems that this one little parameter is cause for much confusion when it comes time for a definition. I guess the pure way of thinking about what it really is, is a measure of available bicarbonate in the water that can be used for corals to take in to use to secrete their calcium carbonate skeletons. But mostly I think it is best thought of as two things. A buffer for pH, meaning that the correct alk (and higher alk ) will help to keep your pH from fluctuating too much. Alk is also a needed component for keeping acroporids as these corals consume alk in order to survive and grow. The school of thought for a long time was that if alk shows how much bicarbonate is available to be taken up by corals and can also limit pH swings, then higher than normal levels would be best. Most people recommended that we keep out Alk levels at 10-12 dKH. Over time myself and many others, keeping primarily acroporids as well as other SPS, found that the high end of the dKH scale is not always better and that keeping alk closer to natural sea water levels of ~8dKH yielded good, if not better, results for SPS. My personal experience is that I found much less incidence of RTN and my pH became just as stable when balanced with the proper levels of calcium and magnesium. So my recommendation is to keep alk around 8-9 dKH for keeping acroporids. Another nice benefit of lower alk was less precipitate on heaters and pumps.

Calcium.
A little easier to define. Calcium is used by our corals to grow. Natural seawater levels are around 380-400ppm. The role that alk and calcium have is that the two of them compete for space in the aquarium. having too much of one will limit what one can have of the other. Generally you can have low alk and high calcium, or high alk and low calcium, and in between the two is that sweet spot that most people try to hit. If you are having trouble getting your alk and calcium values in line you should check out Randy's article on fixing alk/calcium problems it gives some really nice graphs that are helpful.

http://web.archive.org/web/200211270...v2002/chem.htm

Personally I think you should not go below 400ppm on calcium. And I have had the best success with high levels of calcium between 450 and 500 ppm. I feel that this allows me to get a very good growth in my aquarium. I had kept my calcium levels at around 360-380 for a few years and while this did not cause any problems, my growth wasn't anything to brag about. High ca levels really pushed my growth up a huge notch. Note, that I keep low levels of alk in my tank so that helps me to keep a higher level of ca in the aquarium as well.

Magnesium.
In all honesty I don't understand magnesium as well as the other two parameters. I know that corals do take in magnesium so it is needed on that level. But most importantly I know that having the proper amount of magnesium in your reef is essential to maintaining proper alkalinity and calcium levels. Inadequate levels of magnesium can lead to using a tremendous amount of supplements trying to maintain the proper levels of calcium and alkalinity. So if you ever find yourself struggling to maintain alk and ca check to see if your mag levels are adequate. IMO, a minimum level of 1300 ppm should be the goal when it comes to magnesium levels. This is important to know because many, many salt mixes are deficient in magnesium and many times one will have to add magnesium to freshly made salt water prior to doing a water change. Otherwise you magnesium levels will drop with each water change you do.

I personally like to maintain magnesium levels at 1450-1500 ppm. For me that has worked out best. it allows me to easily maintain my alk and ca levels and my corals seem to do best at this level as well.

OK that's it for a little while. Please feel free to comment on anything I have written, please add you own thoughts and experiences as well. I'll soon post in this thread my means of supplementing all of these in my tank as well and my thoughts on what works best for my setup and why I feel that way.

If you have any comments on this thread, or have an idea for another thread please post your thoughts here

http://archive.reefcentral.com/forum...readid=1176047