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JB NY 08/07/2007 02:23 PM

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

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.

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.

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.

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

JB NY 08/07/2007 02:46 PM

Here is my thoughts on supplementing.

For alk only. I have always used Seachem Reef builder. It's not too expensive near me. I only add it when something is out of line with alk only.

For Calcium only. I use Kent's turbo calcium. Again only used when something is out of line with my calcium only

For determining how much of each supplement to use I have been using jdieck's calculator

For both my Calcium and alk needs I use both a calcium reactor and a neilson (Kalkwasser) reactor. You can use two part additives (hopefully people will chime in who use them) but for me I find that the calcium reactor is a set it and forget it setup. Once it is dialed in I only look at it once a week to make sure that everything is working correctly, the rest of the time, I don't even worry about my alk and calcium levels.

If you need an introduction to calcium reactors in general. Here is a short primer that I put together to help you understand the basics.

As to why I use a kalk reactor in addition to the calcium reactor? I like using kalkwasser as it helps me to maintain a higher pH due to the calcium reactors tendency of pulling down the tank pH. Also over the years I have felt that it does help with growth and coloration to a small extent. Meaning that I can generally tell by looking at my tank when my kalk reactor needs to be filled as the corals just look a little bit different. Perhaps some other people can comment on using a kalk and a calcium reactor together. If you have noticed similar things or is it all in my head. :)

As for magnesium. Once I get the main tank up and running with the correct magnesium levels. I only supplement magnesium in the water used for water changes. Other than that I never add it to the main tank. I do weekly water changes, so perhaps the frequent exchange of fresh water helps to keep the magnesium levels from dropping.

Also, I do check the alk/ca/mag levels of a new batch of salt before I do the first water change with it. From here I adjust the levels of the newly mixed salt to match that of my main tank for the remainder of the salt batch.

JetCat USA 08/07/2007 02:48 PM

Agreed for the most part, i have found the best results with Ca between 400 and 450, Alk at 9.6 dKH but Mg a little lower then yours, i keep mine around 1300, I've only noticed problems keeping Ca up when it gets down below 800ish and coral growth I've not noticed a significant difference with it from 900 to 1600.

gary faulkner 08/07/2007 02:50 PM

How often do you test and what brand do you recommend for testing?

Just want to say, glad we are starting with the basics.

naka 08/07/2007 02:54 PM

I think key to success in SPS tank is keeping your parameters stable. I nearly went through entire Salifert ALK test kit while fine tuning my calcium reactor. Now I only test for ALK/Calcium once a week.

I've had problems when my ALK was above 9 for some reason. I've experienced tip recession and stn on few of my corals. Now I keep my ALK around 7 -8 dkh, but never above 8 dkh.

Calcium is one the easiest to maintain for me. It's never been an issue. I keep mine 420 - 440 ppm stable.

I get really lazy when it comes to MG levels. I check mine once a month. I have some MG granules in my calcium reactor, so I don't add any MG to my tank. It's always around 1500 ppm when I test my water.

Nice thread Joe.

JB NY 08/07/2007 03:04 PM

gary faulkner If one of my parameters is not right, I test, dose any additives and retest 24 hours later. Then once everything is correct. I only test once a month. 90% of the time my parameters are almost exactly the same month after month.

Naka I completely agree. I forgot to add that one should strive very hard to not have the parameters vary much, if at all. Stability is a great and powerful thing in a reef tank. Work hard to keep things stable and good things always follow.

For people who are testing junkies, if you are going to do testing more than once a week. I wouldn't do it less than 24 hours apart and I would say to try and test the same time each day.

kev apsley 08/07/2007 03:08 PM

let me just add that I use B-Ionic 2pt for my ca/alk needs. It should be noted that regular testing of both calcium and alkalinity should be done while trying to find that sweet spot.

Also, the bioload will change overtime, as corals grow and and their demand for calcium increases people using a 2pt system need to always be aware that their dosing amounts will also increase to keep up with the demand...test..test...test

jeffbrig 08/07/2007 04:16 PM

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

<a href=showthread.php?s=&postid=10500592#post10500592 target=_blank>Originally posted</a> by JB NY
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.

The primary benefit of Mg is that it allow calcium and bicarbonate levels in the water to exist at supersaturated levels. In laymen's terms, having high Mg allows you to maintain higher Ca/Alk.

Because Ca and bicarbonate are supersaturated, they are always ready to fall out of solution. This is the abiotic precipitation that every talks about on heaters, pumps, and solid surfaces. As calcium carbonate forms on these surfaces, Mg is also able to bond with it. By doing so, Mg blocks Ca and bicarbonate from being able to attach, significantly slowing the rate of precipitation. If you let Mg drop, you have to pour in more and more Ca and Alk supplements, and precipitation becomes more and more of a factor.

I don't think corals deliberately use (or require) Mg, it's more of an incidental pick-up while building their skeletons. But, maintaining Mg levels is necessary to hold Ca and Alk levels where you want them.

cham 08/07/2007 04:25 PM

Great article.

I use homemade two part made from Baking Soda & Ca chloride. I also use MAG flake & Epsom but like JB NY I rarely ever need MG supplimentation. Reef Crystals does a pretty good job.

I however prefer to dose my sps system with two part & kalk. I dose the two part using reef dosing unit and a 5 gallon jug for CA & another for ALK. I set my dosing rate, test like a mad man for a couple few weeks to see if its too much or too little and at that point it is "set it & forget it" for me too.

I also run a lower PH naturally (C02 levels in the home) that I have tired to remedy with an air pump bringing in outside air into skimmer intake with no great help. So to add a CA reactor to a system that already runs 7.9 to 8.0 daily swing didn't seem like a good alternative to me.

I also use kalk in my ATO at full saturation controlled by a PH controller & dual float switch so that my kalk is only dosed when PH falls below a certian level and turned off once PH gets back up or the sump reaches a pre set height.

Once my demands on my tank increases, its as easy as turning a knob on my doser to increase my rate from 10 ml's to 15 or 20 as shown on the LED display. It will dose all the way up to 500 which IIRC is up to 85 ml's per hour per channel. Would be awesome to have a system that needs that type of supplimentation. :)

Scuba Dog 08/07/2007 04:59 PM

I have a great deal of experience with chemical testing and the normal day to day operations of a multi million dollar chemical production unit. A sps tank and a chemical plant have a lot in common with all the equipment, maintance, reactions, and testing.

I learned that its better not to over test(repeated redundant sampling) that can leed to unnecessary adjustments, though a falty test result. In other words dont let a falty result cause you to get your tank out of balance.

When you make an adjustment it is better to make a small adjustment then sit back an wait a day or two for the system to stabilize(knee jerk reactions can be a killer).

My recomendations for maintaining alk, ca, Mg is to get a quality test kits, and keep them in a cool dry area, and keep in mind that over time the reagents in the kit can and will go bad. Also develop a good consistant technique for your titrations. Titrate slowly till you think you hit end point( color change) then add a couple more drops to make sure. If you get a bad result or one that just dosent make sence then retest and see if you can reproduce the number. Who know it could be an accurate result then its time to go trouble shooting and inspect your equipment.

In my opnion in brine chemistry its way better to go slowly on setting up calcium reactors and kalk stirers, even when dosing two or three part additives. At least until you have a real good feel on how your system is performing

Cultivatedcoral 08/07/2007 06:00 PM

I keep my alk at 6-8 dkh, Ca at 430-450 and MG 1300-1400 and postassium at 380-400. Sorry had to at that too. My name is zeorocka!! haha

teen 08/07/2007 07:52 PM

is it true that low levels of magnesium can lead to poor colors in sps corals? my alk and calcium are in line, but i dont test for magnesium, and im thinking its on the low side. recently ive been having some browning issues, and i dont know what to blame it on.

gasman059 08/07/2007 07:58 PM

I look at them as the holy trinity. All 3 go hand in hand and IMO should be measured consistently.

Philwd 08/07/2007 08:24 PM

I recently let my Mg levels get low. ~ 960. My testing had gotten sporadic as it always tested 1350. I had started getting tip recession and blamed it on alk. Now that the Mg is back in line everything thing is getting back to normal.

TandN 08/07/2007 09:40 PM

This is a great thread and yes Stability is KEY I just wish there was a more reliable ALK test kit

Sk8r 08/07/2007 09:43 PM

I am in a bit of a situation, or I landed in one, when I moved, had my rock crash and cook because of a delay in setup: I had to go ahead and put all my corals [held at my lfs] into a raw new tank, and I lost the mille. Bear with me: this does somewhat bear:

I have always dosed Kent Turbo Calcium, Kent Mg, and Kent Dkh Alkalinity Buffer, testing every 3 days, never able to get cal much above 400, mg about 1200, alk about 8.3 no matter what I the old setup.

Knowing I was in trouble, I set up a 20g refugium, got a kalkreactor, and now maintain a much steadier 420 calcium, 9.3 alk, and about 1400 mg. The surviving sps are beginning to come back, not yet regrowing rtn'd areas, but thickening tissue in 'good' areas and turning quite strongly green/orange, etc, as appropriate---acropora aculeus [I think] and a definite several montiporas: as yet not a bit of polyp extension, but phosphate levels are dropping significantly [kalk is alleged to precip it out: don't know, but it is dropping, since algae is going away.]

I'm pretty steady at 420 c, 9.3 alk, and 1400 mg, and I'm liking that level, based on the reaction of some really badly abused sps. I'm determined to get this tank back on track post-move, and I'm happy to hear others opine that that's not a bad range to be in.

What else has changed for me is stability. I'm only a 54g, with a 30g sump/refugium, and I've gone from a daily dose and 20 point flux in most readings, to no flux to speak of. Being as small a tank as this is, the kalk is able to hold it steady, with only once a month dosing, and I think this is going to be a vast improvement over my old situation, [I had buffer supplied by the topoff, but had a fierce alk build-up, over time: I know everybody says if you get an alk spike it's harmless and just let it fall naturally---but I lost 4 acroporas in that period. So if I ever get another such alk spike [though the old method of dosing is now done-with] I will be much more aggressive about remediating it with water changes. My current goal is not to let such things happen.

ReefWreak 08/07/2007 10:17 PM

Sk8r sorry to hear about your problems with alk spikes, however it's not an uncommon problem, usually with disasterous results. A local wasn't paying enough attention when he set up his calcium reactor and as a result got an alk spike that killed a few of his corals in his tank. I've heard similar stories from people around RC as well, so it's not uncommon of a problem.

JBNY thanks again for another great discussion piece, as your tutorials have always been helpful to myself as well as many, many other beginners. It's amazing the things we learn in this hobby whether it be about biology, chemistry, or nature in general, our knowledge is strengthened by people like you who make an effort to round up the information to be easily passed through the ranks in an effort to increase success across this whole hobby.

Stability FTW. I'm still dialing in my CA reactor so I can run with the big dogs :)

dukes707 08/08/2007 06:37 AM

i agree with Gasman059 about the sps holy trinity being cal/alk/Mg. they all share a relationship, although nonlinear in some cases, all are relative to eachother in respect to keeping things stable. all should be tested and kept as stable as possible.
i use kalkwasser in an ATO for all top off water. pH stays rock solid @ 8.2. i recently got through a bout with wack alk due to a faulty salifert kit i had and my Mg was off by a large margin due to using only kalk as my cal/alk additive. i wasent aware of the amount of Mg depletion that occurs with using only kalk, and i paid for it. and got an API for alk.
thanks to randy's informative articles on mg and kalk i was able to remedy the situation before losing too many sps'. some are still recovering from the subsequent brown out. my alk fell to about <6 but after correcting my mag levels with randys two part #3 mag supplement mix and supplementing with some bakng soda after about a lil over a week things are finally getting back to relative normal.
word to the wise, whatever supplementation system you use make sure you understand it completely, pros and cons. read as much as you can on whatever system you are using.
now that things are stable again, and polishing waterchange water with Mg additive prior to changing things are rock solid.
cal~400 alk~8.5 mg~1350 pH-8.2 steady. i like to ry to keep things as close to NSW, and my critters seem to appreciate it more than keeping things supersaturated and at the high end of the params. my experience with my system and what supps i use.

Aquarist007 08/08/2007 08:42 AM

I really appreciate what I have read so far--thanks.

I am still trying to grasp my fluctuating pH over a week it will drop from 8.3 to 7.7. I am aware that carbon dioxide plays a big part in this. However I just read above that a stable alkalinity level will help maintain the the stability of the pH level. My alkalinity has been stable at 8.5----and in the past I have had it as high as 13.dKh(stable) but the same fluctuation in pH occurs?

Opening windows etc will raise the pH slightly but not really that much. I used to use the kent reef builder but I am aware that it raises the alkalinity also(this is how I ended up with 13 dKH)
I am also aware that I could use Kalkwasser to build up the pH and not the alkalinity.
I am confused at what route to take?

Sk8r 08/08/2007 09:24 AM

This is what I know about supplementation: if you hand-dose, you need to test at the same time every day to try to minimize the swing. I got into serious trouble letting an unstirred 7g ro/di bucket do my alk supplement. Bad idea. That let to, eventually, a buildup that finally got dosed when the bucket ran low: hence the spike.

A kalk reactor, supplying both alk and cal, can contribute to ph problems, but I can say my gallon + a day evaporation rate and small tank size [54g] makes an ideal situation for kalk as THE supplement---so far. Corals can get very hungry, and once the fast-growing montiporas really get started, it may be different, but right now the reactor will hold the 54g steady with only set-up dosing.

Some people run both a calcium reactor AND kalkreactor.

And stability I'm sure is a big item in the benefits. That and precipitation of phosphate via kalk [unproven, meaning I've never found any article with research] tank algae is going away.

Does anybody know whether the ocean has 24 hour cycles in ph, alk, cal? Is there any net effect of dark period and coral absorption cycles re the condition of the water in the immediate surrounds of a reef?

JB NY 08/08/2007 01:31 PM


<a href=showthread.php?s=&postid=10503028#post10503028 target=_blank>Originally posted</a> by teen
is it true that low levels of magnesium can lead to poor colors in sps corals? my alk and calcium are in line, but i dont test for magnesium, and im thinking its on the low side. recently ive been having some browning issues, and i dont know what to blame it on.
I've never seen low mag cause browning issues. My mg was at 900 for a long time before I caught it. None of my corals were brown at the time.

capn_hylinur Sometimes if you are pushing your ca reactor too hard it can cause lower tank pH. The only suggestion is to try and dose some kalk at night. I used to mix a teaspoon of kalk with a little ro/di water and just tossed it in the sump. I did that a few years back when I was having large pH fluctuations. The ultimate solution was to get a different ca reactor that didn't have to work so hard, but that's another story.

JB NY 08/08/2007 01:34 PM

Yeah getting the right amount of dosing can be challenging and as many people wrote, the more your corals grow the more demands are placed on the tank so you need to adjust things. Sometimes when adjusting you find the parameters bouncing up and down till you get things stable. It can be frustrating trying to get things dialed in but once your do. The tank does well. Getting everything stable is key though. Everyone has brought up that point but it is very true.

Keeping the parameters is nice, keeping it all very stable is great!

Randy1 08/08/2007 06:21 PM

One thing you don't want to do is wait till your levels are off to add anything Cal. or Alk. or mag. You need to detemin your demand. I have settled in with 1 cup of 2 part calc. and alk. daily and 1 cup of mag 2 part twice a month. If I add some corals then I'll begin monitoring these levels and adjusting upward as needed. You should add calc. and alk. daily to keep it stable.

Sk8r 08/08/2007 06:39 PM

I'd add: a log book is your friend. If you keep a log of what you added and what the reading was on the following day, you can spot trends and correct before you're into bad territory.
You also learn how your particular tank reacts, and you can smooth out the peaks and valleys of calcium/buffer.

solbby 08/08/2007 07:15 PM


<a href=showthread.php?s=&postid=10501353#post10501353 target=_blank>Originally posted</a> by jeffbrig

I don't think corals deliberately use (or require) Mg, it's more of an incidental pick-up while building their skeletons. But, maintaining Mg levels is necessary to hold Ca and Alk levels where you want them.

All protein synthesis, DNA replication and most enzymatic process use Mg as a co-factor. It is incredibly important for biosynthesis.

Not trying to be nit-picky just bringing a thought to the table, :) .

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