Myka's Guide to Calcium, Alkalinity, Magnesium, pH, and Salinity

[Myka]

I posted this article up on some other forums a few years ago, and have had a couple people ask me to post it up here on SaskReef. I hope it can help some of you out.

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Calcium, alkalinity, and magnesium are the backbone of your reef. This Guide will explore the relationship between these three elements (and a couple others) by simplifying the information, and presenting it in an easy to read and understand short format that hopefully won’t bore you too much. I would also like to point out that even though some seasoned reefers may pick up a tid bit of info here and there in this guide, it is mainly aimed at novice reefers to give them a good starting point.



Topics:

~ The Importance of Test Kits
~ Calcium
~ Alkalinity
~ Balanced Calcium and Alkalinity
~ Magnesium
~ pH
~ Waterchanges , Salinity, Specific Gravity, and Temperature
~ Dosing


The Importance of Test Kits

Good quality test kits are very important, and I would suggest you spend the extra few bucks on at least a few good quality kits for your reef tank. The most important would be calcium, alkalinity, magnesium, and nitrate; for which I would suggest the use of Salifert at least. I by far prefer Elos for calcium and alkalinity, but I find Salifert just as good as Elos for magnesium. The new Hanna Alkalinity Checker is getting great reviews as well although I haven't tried it myself yet.

pH test kits aren't overly accurate, so I would suggest you either don't worry about it (explained later) or buy a hand held pH meter (about $60) or pH monitor (about $120). pH meters and monitors are notorious for burning out probes. You can expect the probe on either to last a couple years, any more than that and you're a lucky one!

An ammonia kit is a great indicator like the nitrite kit, and imo is necessary when cycling your aquarium, and a handy tool to use for figuring out what's going on when things are amiss. I prefer Nessler test kits as opposed to salicylate test kits for ammonia. Nessler kits read only toxic ammonia (NH3) while salicylate kits test both toxic ammonia and ammonium (NH4) which is not toxic for your reef. If you ever have the need to use an ammonia detoxifier like AmQuel or Prime you will need a Nessler kit to accurate test the ammonia after using those products. Those products will produce a "false" positive on a salicylate kit. API used to offer both a NH3 kit and a NH3+NH4 kit, but now oly offers the salicylate kit. The only Nessler kit on the market that I know of that is easy to obtain is the SeaChem Ammonia kit. You can also use SeaChem Ammonia Alerts.

Nitrite isn't overly important in a saltwater aquarium because nitrite is not toxic in saltwater the way it is in freshwater so you don't really need a nitrite kit. Nitrite very rarely gets to a high enough level in an aquarium that it is even vaguely toxic (think a hundred ppm). There is little need for a nitrite kit, but it is a great indicator as to where you are in your cycle when first starting your aquarium, and in mature tanks it is an indicator that something is amiss.

Nitrate is another important nutrient in the tank. I would suggest either Salifert or Elos. Using either of these kits, nitrate should be no higher than 5 ppm, but essentially it should be undectable on these kits.

For phosphate the Salifert or Elos regular sensitivity are both fine. When using these kits phosphate should be completely undetectable or it is too high. For those more serious reefers you should consider the D-D Merck high sensitivity Phosphate kit (about $80) or the Elos High Sensitivity Phosphate kit. Phosphate would be the number one cause of brown corals and algae growth, with nitrate as a close second. The new Hanna Phosphate checker is also receiving great reviews although I have not used it myself yet.



Calcium:

Calcium is used by all corals with a skeleton (SPS and LPS), clams, calcareous algaes (coralline, halimeda), and even invertebrate to build their shells. Generally, natural seawater contains a calcium level of 410 ppm [as per Randy Holmes-Farley]. A calcium reading of lower than 360 ppm can compromise coral growth. Having more than 450 ppm calcium is a waste of additives, and if you take a look below at the balanced ratio to alkalinity, a high calcium level requires a very high alkalinity level! Studies have shown that an elevated calcium level does not increase corals’ growth rate or density.

If you dose too much calcium in one go while your alkalinity is too low you can cause the calcium to precipitate out which looks like a snow storm in your tank, and instantly pulls a bunch of calcium and alkalinity out of your water. You will have to re-dose. When you dose calcium, the alkalinity level will drop slightly. I like to keep my own tank’s calcium between 415-425 ppm.

I prefer to dose calcium before alkalinity (provided alkalinity isn't lower than 6 dKH, otherwise dose alkalinity first), and magnesium before both of these. Dose in a high flow area, and make sure the slurry is diluted before it touches any corals as the slurry will immediately burn corals.



Alkalinity:

Alkalinity is what we use to measure bicarbonate as test kits for bicarbonate would be difficult and expensive to obtain. Alkalinity in (very) short is salt water’s ability to buffer the pH against acids which try to lower the pH. Generally, natural seawater contains an alkalinity level of 7 dKH. Corals use calcium and alkalinity in equal parts to create their skeletons, which works out to be 2.8 dKH for every 20 ppm of calcium.

Low alkalinity can be one of the factors of nuisance algae growth. Both low and high alkalinity levels can cause precipitation of calcium. Low alkalinity causes precipitation in the water, while high alkalinity causes precipitation on heat sources like heaters and powerhead impellers.

When you dose alkalinity you will notice that it affects your calcium level by slightly decreasing it. When alkalinity is allowed to fall you will notice that your calcium will rise slightly in comparison causing an imbalance. Alkalinity will be the most challenging to keep consistent. Check it often, and dose as required; this will also help to keep your pH steady. To match the calcium level of 410-420 ppm I like to keep in my tank, I like to keep my alkalinity at about 7-8 dKH.



Balanced Calcium and Alkalinity: (as per Randy Holmes-Farley)

360 ppm to 0 dKH
370 ppm to 1.4 dKH
380 ppm to 2.8 dKH
390 ppm to 4.2 dKH
400 ppm to 5.6 dKH
410 ppm to 7 dKH (natural seawater)
420 ppm to 8.4 dKH
430 ppm to 9.8 dKH
440 ppm to 11.2 dKH
450 ppm to 12.6 dKH
460 ppm to 14 dKH

The relationship between calcium and alkalinity is an important one, and the numbers need to be balanced for optimal absorption by the corals and other life much like the human body needs a balance between calcium and phosphorus to make good bones. Some people may experiment with elevating the alkalinity level beyond the balanced ratio to try to increase coral growth, but there is no proof of this theory. Keep an eye on your calcium level though if you experiment like this as it may decrease your calcium, and may make it difficult to keep your calcium at an acceptable level. Also keep an eye on the precipitation on heat sources as this becomes a waste of your calcium and alkalinity dosing efforts. My aquarium’s alkalinity shot up to 18 dKH at one time, and at this point some corals did show irritation, but nothing was lost.



Magnesium:

Magnesium both helps to buffer the pH from falling, and reduces the precipitation of calcium. Think of magnesium as the fulcrum of a teeter totter. Without magnesium at the level it should be, it is difficult to keep calcium and alkalinity at a steady and proper level. Natural seawater generally contains 1280 ppm of magnesium. Low magnesium can be one of the factors of nuisance algae growth, and most reef keepers agree that 1350 ppm works best in our little glass boxes. I prefer to dose magnesium to ~1350 ppm before adjusting calcium and alkalinity.

[Myka]

pH:

Natural seawater has varying levels of pH but is generally between 8.0 and 8.3. pH is the concentration of hydrogen to hydroxide ions in a solution. Do we care about that technical stuff? Not really. Let me explain...

I’m going to just barely touch on pH as it is a bit of a difficult thing to fully understand, and is affected by so many elements and situations that it would only be confusing to try to explain it all. The important part to know is that pH is affected by your alkalinity and magnesium levels, and also greatly affected by the acids produced when organics break down (nitrogen cycle). Another thing to note is that if your house contains certain levels of CO2 (much lower than is poisonous to humans) from you and your pets breathing in it, this can cause the pH to drop in your tank as the CO2 in your house mixes with the aquarium water. CO2 is acidic, this is why it is used to break down the calcium carbonate in calcium reactors. If you find in the winter your tank has a lower pH than in the summer this may be due to you not opening your windows for fresh air in the cold winter months, and having the levels of CO2 build up in your home. High aquarium temperatures also cause the pH to drop.

Many people struggle with low pH in their tank. This is often caused by a large amount of waste breaking down in the aquarium creating acids, or high levels of CO2 in the house (and hence in the aquarium). Low alkalinity can also be a factor, but on its own wouldn’t be the main culprit. Often you can raise your pH just by adding an airstone (or protein skimmer). The way I see it, is make sure your calcium, alkalinity, and magnesium are at acceptable levels, that your house and tank get plenty of fresh air, that you have a good protein skimmer and good circulation with powerheads to reduce the amount of waste breakdown in the tank (keep detritus suspended instead of settled), and your pH should gradually stabilize at an acceptable reading over the first 6-12 months the tank is setup. A fluctuating or low pH during the cycling of your tank is normal, and should correct itself after the cycle is finished and you have done a couple waterchanges, but may take a few months.

You may notice that your tank has a lower pH early in the morning than last thing in the photo period. That is normal. The organisms in your reef respire, and create CO2 at all times of the day and night. During the photoperiod the reef's organisms are using light energy to process CO2 and water into carbohydrate and oxygen. This process is called photosynthesis. As you know from reading above, as the levels of CO2 increase in the aquarium the pH drops, so when the lights are out, and photosynthesis is not happening there becomes an abundance of CO2 in the aquarium which causes the drop in pH at night. If the swing in pH is rather large, then you can add a refugium/algae chamber to your sump with chaeto, and run the lights on the refugium so they are on when the tank lights are off. Be sure the refugium lights don’t leak too much light into your display tank though.

My take on pH is leave it alone. Unless it is really out of whack, don’t mess with it. It is easy to change, but difficult to keep steady at a level that it doesn’t want to be at. This is one of those times where natural adjustments (fresh air, reducing organics, airstone, etc) is much more beneficial than chemical adjustments. A fluctuating pH level is much more detrimental to a reef than a low or high pH. If it is between 7.6 and 8.4 I say leave it alone, don’t screw with it. It ain’t broken, don’t try to fix it!



Waterchanges , Salinity, Specific Gravity, and Temperature:

Natural seawater (with the exception of the Red Sea and brackish areas) has a usual salinity of 35 ppt or specific gravity of 1.0264 which works very well in our reef aquariums.

Most of the corals we keep are collected from water which ranges from 82-86 degrees. Many people believe that we should mimick this, however our aquariums have limitations that aren’t expressed in wild reefs. The most important limitation is waste removal, which we do by filtration and protein skimming. Keeping high temperatures in our aquariums only achieves increased metabolic rates of the aquarium’s inhabitants which creates more waste. This is why a lower temperature of 76-82 in our aquariums is much more optimal.

When doing waterchanges get your fresh saltwater mixed up to the proper specific gravity and allow the water to circulate and match the temperature of your display tank with a powerhead and heater for 24 hours. It takes time for the pH of the new saltwater to stabilize, and aerating for 24 hours is a safe way to be sure of this. Retest the specific gravity after 24 hours and adjust as needed. Test the calcium, alkalinity, and magnesium levels with every new bucket of salt (roll the bucket several times to mix the salt before using it). Adjust as necessary with additives, then proceed with your waterchange. By doing your waterchanges this way, it is often unnecessary to dose your aquarium between waterchanges if you don’t have a high calcium and alkalinity demand, and do waterchanges often enough. This practise reduces the risk of overdosing your tank. It is good practise to figure out how often you need to do waterchanges to maintain your calcium, alkalinity, and magnesium levels without dosing your aquarium. However, it is impossible to maintain calcium and alkalinity levels in high demand reefs, and daily dosing will be required.



Dosing:

The number one rule for dosing is do NOT (like never, ever, ever) dose for anything you don't test for. That would be like filling your car with oil, and not checking the level. Too much and you blow the seals in your engine...too little and your engine will seize.

For large tanks, high demand, and/or mainly SPS tanks I would suggest the use of a doser. Some people with mid-sized tanks like to use Kalkwasser either by drip, a dosing machine, or a Kalk reactor/stirrer. Kalkwasser works quite well as it doses both calcium and alkalinity in proper ratio. Be aware that you will still have to supplement Magnesium when you dose Kalk. I personally do not like calcium reactors as I find they have a tendency to lower pH (by the use of CO2) and I feel dosers are easier to fine tune. Kalkwasser has the added benefit of increasing pH and is often dosed at night to compensate for the nightly pH drop.

There are also some two part solutions out there which can be setup as drips, on dosing machines, or dosed by hand. The two part solutions are made in complimenting saturation so that you use the same measure of each solution. This can be a very simple solution to calcium and alkalinity dosing especially for novice aquarists. When using Kalkwasser or a two part solution you will have to initially adjust your calcium and alkalinity with individual additives to the proper level, and periodically to prevent imbalance.



In the case of dosing there are some products out there that I feel are superior to others:

~ Two Little Fishies C-Balance (my first choice for liquid 2-part dosing)

~ Fauna Marin Calcium carbonate (my first choice for calcium dosing on any size tank)
~ Bulk Reef Supply Calcium carbonate (second choice)
~ Kent Liquid Calcium (for smaller tanks, pricey but easy to use)
~ Kent Turbo Calcium (for medium-sized tanks, or smaller tanks with higher calcium demand)

~ Fauna Marin Sodium bicarbonate (my first choice for alkalinity dosing on any size tank)
~ Bulk Reef Supply Sodium bicarbonate (second choice)
~ SeaChem Reef Buffer 8.3 (alkalinity dosing for sm/med tanks that tend to have low, high, or fluctuating pH readings)
~ SeaChem Reef Builder (alkalinity dosing for sm/med tanks with acceptable pH readings)

~ Fauna Marin Magnesium chloride used 8.5:1 with Epsom salt (8.5 parts MgChl and 1 part Epsom for balance)
~ Bulk Reef Supply Magnesium chloride
~ SeaChem Reef Advantage Magnesium
~ Littlesilvermax's Magnesium mix 8.5:1
~ Buy Magnesium sulphate (Epsom salt) in the pharmacy for mixing with Magnesium chloride. Mg sulphate is NOT acceptable for dosing solely.

~ RowaKalk Kalkwasser



For continued reading on these subjects check out Randy Holmes-Farley, the reef aquarium chemistry guru.

Feel free to suggest some additional information to the Guide, or if you have questions I can do my best to try to answer them.

[Pan]

two little fishies the best? really you think so? which ones have you put against it that it came out on top?

[fkshiu]

Originally Posted by 'Ol Nobodaddy

two little fishies the best? really you think so? which ones have you put against it that it came out on top?

I tend to agree. You should mention that ALL such name brand additives may be had for far cheaper if purchased as bulk chemicals since, for example, all calcium additives are basically Calcium Chloride, and all magnesium additives are Magnesium Chloride or Magnesium Sulfate (or a combination thereof) etc etc.

Any discussion of key tank parameters is incomplete without mention of Randy Holmes-Farley and his numerous very insightful and very useful articles on the subject.

[Pan]

Originally Posted by fkshiu

I tend to agree. You should mention that ALL such name brand additives may be had for far cheaper if purchased as bulk chemicals since, for example, all calcium additives are basically Calcium Chloride, and all magnesium additives are Magnesium Chloride or Magnesium Sulfate (or a combination thereof) etc etc.

Any discussion of key tank parameters is incomplete without mention of Randy Holmes-Farley and his numerous very insightful and very useful articles on the subject.

Yep, Randy's articles are all in my chem folders seachem, kent etc are just charging a premium for what one could do on a saturday night...come on who has mixed chemicals into baggies on a saturday night

I think two part is a better idea than reactors...at least for me reactors have become old hat...

[fiorano]

thanks so much for all this info myka

[Myka]

I am glad my piece was mostly well accepted. Kind of a touchy subject since people have so many different opinions on this one. Thanks for the reviews, and those who show appreciation.

Originally Posted by fkshiu

I tend to agree. You should mention that ALL such name brand additives may be had for far cheaper if purchased as bulk chemicals since, for example, all calcium additives are basically Calcium Chloride, and all magnesium additives are Magnesium Chloride or Magnesium Sulfate (or a combination thereof) etc etc.

Any discussion of key tank parameters is incomplete without mention of Randy Holmes-Farley and his numerous very insightful and very useful articles on the subject.

Personally, I am not a fan of bulk chemicals for reef keeping, and I regret to say that I can't even explain why very well. I have found over the years that "most" tanks that use bulk chemicals instead of aquarium designed products seem to lack a bit of pizazz. I am sure you could find 500 photos that would prove otherwise, and I would be hard to disagree. However, in my experience I find aquarium designed products outperform bulk chemicals, and I don't know why.

I suppose mentioning Randy Homes-Farley would be a great "for continued reading on the subject, refer to...". This article was written for those who want something simple, and straight forward where Randy's articles are usually quite in depth, and are anything but basic. I will add this though, thanks!

Originally Posted by 'Ol Nobodaddy

two little fishies the best? really you think so? which ones have you put against it that it came out on top?

I really like the C-Balance product. Without listing the different "raw chemical" two-part solutions as I believe that most all aquarium designed two-parts are far superior to most all bulk chemical two-parts I would place TLF C-Balance over Kent Tech-CB, ESV B-Ionic, Salifert All-In-One, and AquaC Complete. I quite like the KNOP products, but they don't really have a two-part.

[fkshiu]

Originally Posted by Myka

Personally, I am not a fan of bulk chemicals for reef keeping, and I regret to say that I can't even explain why very well. I have found over the years that "most" tanks that use bulk chemicals instead of aquarium designed products seem to lack a bit of pizazz. I am sure you could find 500 photos that would prove otherwise, and I would be hard to disagree. However, in my experience I find aquarium designed products outperform bulk chemicals, and I don't know why.

I really like the C-Balance product. Without listing the different "raw chemical" two-part solutions as I believe that most all aquarium designed two-parts are far superior to most all bulk chemical two-parts I would place TLF C-Balance over Kent Tech-CB, ESV B-Ionic, Salifert All-In-One, and AquaC Complete. I quite like the KNOP products, but they don't really have a two-part.

Fair enough. I believe it's called the power of "branding"

[Treebeard]

Finally an explanation of the relationship between these elements that I can understand. (well...almost!) Thanks for the great information Myka. I have bookmarked all 3 of them for future reference.

[Tom R]

Thanks Myka

Your take on this important info is much appreciated.

Tom R