Kalkwasser

[jhnrb]

-Preparing Kalkwasser

The more hobbyists you listen to, the more methods you will come across about how to prepare Kalkwasser (Limewater) in the proper manner. This is unfortunate, as it is confusing for beginners. There really is no one manner in which to prepare Kalkwasser ideally.

All methods advocated are really not that much different from one another. Some hobbyists may use a little more calcium hydroxide and others may use a little less. The concensus, though, is that the chemical to use is calcium hydroxide (and not calcium oxide).

Here is just one method to consistently obtained KW with a pH of over 12.2, and a pH that maintaines itself.

-How is this done
Using treated water, that has gone through a reverse osmosis filtration unit and then through a silicate removing compound add 3 level teaspoons of calcium hydroxide, per gallon of water then very gently stir the mixture. Not forcefully, just gently, to mix the powder with the water evenly. The reason to mix it gently is to prevent (or minimize) the amount of carbon dioxide that gets into it. After finishing mixing, powder settles to the bottom of the vat. That is normal since not all powder will dissolve. Water can only absorb so much calcium hydroxide before it becomes saturated. This is a chemical fact. Note, also, that cold water absorbs more of calcium hydroxide than lukewarm water or warm water.

-What should the pH be
After preparing Kalkwasser this was and testing it, a pH of over 12 is obtained consistently. This is very good as saturated kalkwasser water has a pH of around 12.4.

In any event, regardless of what you do, you must ensure that as little carbon dioxide as possible gets into the water and calcium hydroxide mixture as this would result in the formation of calcium carbonate that will settle to the bottom, and does not dissolve. This process also lowers the pH of the mixture, which is not desirable.

For a better and consistent mix, dispose of the excess powder and use fresh powder for each batch of mix. Not absolutely neccessary but recommended.

 

[jhnrb]

Another View Of The Use Of Kalkwasser

Kalkwasser, Carbonate and Clumping

This article appeared in MFM Dec 97

The following has become a typical scenario for a number of reefkeepers: "I am adding tremendous quantities of kalkwasser but my calcium level the next day is even lower. I am adding buffer like crazy but my carbonate alkalinity won't come up. In fact, the next day everything is low and the pH has taken a dive also! Now I am going to add one of the ionically balanced calcium and carbonate additives... nothing happens, except that I am growing "chalk" deposits on my plumbing and my substrate is clumping."

If this sounds familiar you have established what could best be explained as an artificial instability within your reef system. What these systems have in common is what I would describe as the excessive use of kalkwasser. What is excessive? In my opinion, excessive is when you try to control, with kalkwasser, any aquarium water parameter other than dissolved CO2. This includes trying to use kalkwasser to control the calcium level. Note that this is far from stating that kalkwasser is not, or may not be, beneficial to a system as I will explain later. But first, to get your system back on an even keel we need to explore what the major chemical and mineral players are and how they interact. In this discussion I will assume that what a reef aquarist desires is supplemental calcium carbonate for coral skeletal growth while otherwise maintaining normal sea water parameters.

The typical marine buffer powder is either totally or primarily composed of sodium bicarbonate... baking soda (some contain an added carbonate source and/or a borate). This is a very effective way to quickly raise the buffering capacity, carbonate alkalinity, pH, and stability of a system. It may be just baking soda but it is hard to improve for effectiveness. The by-product is an excess of sodium ions.

Calcium chloride (sometimes sold in supermarkets as a pickling ingredient) is utilized by many of the concentrated calcium supplements. It is a substance that is tremendously soluble in water and therefore able to deliver high amounts of calcium to a system without effecting pH. The by-product here is an excess of chloride ions.

By now you may be thinking "hey, what if I mix sodium bicarbonate or carbonate and calcium chloride together in stoichiometrically correct proportions, wouldn't that supply both calcium and carbonate for my corals?" Yes, and this is the gist of the balanced calcium carbonate supplement. The major by-product here is an excess of both sodium and chloride, the two primary ionic components of sea water, which effectively raises salinity but does not create any ionic imbalances to speak of because the other components of sea water are relatively minor. If a manufacturer adds the remaining components of sea water in such a way that they don't react, you will get a residual of artificial sea water. These products are sold in two containers so as to keep the concentrated Ca++ and CO3-- separated and not form crystals before use.

Aragonite, on the other hand, is a naturally occurring biogenic (life formed) mineral that reaches equilibrium with sea water at a pH of 8.2. It also automatically dissolves into its primary components of calcium, carbonate, and strontium when the pH falls below 8.2 (the natural pH of sea water) thereby driving the pH back towards 8.2 with a slight excess of strontium ions.

Calcite (limestone) is a less soluble mineral form of calcium carbonate that is mined from dry land in a variety of locations. It can be precipitated at a much lower pH than aragonite and is only held in solution in normal sea water by the presence of magnesium ions. Its equilibrium pH of about 7.6, and tendency to co-precipitate magnesium, can make it an unpredictable visitor to your reef system.

All of the problems described in the first paragraph stem from the deviation of aquarium water from the carbonate equilibrium. You see, if the concentration of calcium ions and carbonate ions in a system exceeds the ability of sea water to hold it in solution (supersaturated) it will come out of solution in the form of a solid crystal (precipitate). You can exceed the ability of sea water to keep carbonate in solution in a number of ways.

Calcium supplements and carbonate buffers are more soluble than calcium carbonate mineral. Therefore the addition of these components to your system in excess of normal sea water values will supersaturate an aquarium with these ions and the potential for crystal formation is initiated. This is normally a relatively gentle pressure.

Heating normal sea water will cause supersaturation and precipitation of calcium carbonate. In nature this is not really seen in reef situations but may be a factor in the development of lime muds in the proximity of sea grasses probably at low and slack tides.

Removing the magnesium ion from normal sea water will facilitate the precipitation of calcite. This can be a great concern as pink coraline alga are high in magnesium (therefore drawing magnesium out of aquarium water) and some salt mixes are reputed to be deficient in magnesium to begin with.

Finally, the easiest way to supersaturate sea water and grow crystals is to raise the pH above the pH of natural sea water, 8.2, which is what kalkwasser will do once it has reacted with all the available CO2. In a well maintained and well circulated reef tank, without a lot of fish, there is not that much dissolved CO2 to begin with. Therefore, the addition of kalkwasser, especially in batch doses, can have an immediate and profound effect on aquarium pH and degree of supersaturation. How many of you find the water clouding up at least locally after the addition of a large amount of kalkwasser? That is the formation of tiny calcium carbonate crystals, from the ionic calcium and carbonates present in your aquarium water, by the elevation of pH.

All these processes can occur separately but everything is amplified by the concurrent use of these additives especially with the subtraction of dissolved magnesium from the system. Here is what I believe are the chemical events leading to the destabilization scenario that I described earlier in the first paragraph: A system starts out healthy and stable with the judicious use of one or two of the above described additives and an aragonite substrate. However, with the constant and gradual subtraction of magnesium from the system by the growth of pink coraline algae, decreasing frequency of water changes, and the possibility of magnesium deficient salt mix all conspire to drop the magnesium ion level in a system. With the magnesium level lowered, what was fairly stable system maintained at a pH level of 8.3 by kalkwasser, is now less so, and it is easier to precipitate calcite out of a system in the form of crystals so small they are not noticed immediately. As calcite (not aragonite) will co-precipitate significant quantities of magnesium, the magnesium drain on a system is thus amplified.

(Cont. to part 2)

 

[jhnrb]

Another View Of The Use Of Kalkwasser

(CONT. FROM PART 1)
PART - 2

Your test kits are telling you that while you are still above ocean levels for calcium and carbonate ions, it is not as high as it was a month ago and yet you have not changed any procedures. Time to add more kalkwasser for calcium and a buffer to improve your dKH! But since kalkwasser is not a very concentrated form of calcium, you have to add a larger quantity than usual to match the buffer (bicarbonate) you have just added. But that larger quantity of kalkwasser has raised the pH to 8.4. That, along with the higher concentration of carbonate, creates a higher level of calcite crystal formation with the further depletion of magnesium and, since calcite will reach an equilibrium pH value in the mid 7's, in a few days you are below the pH, calcium and dKH levels of normal sea water! This after you just had the system chock full of calcium, carbonate and a pH of 8.4! ...Time to really hit it now! You greatly exceed manufacturers recommended limits of every calcium and carbonate source you can find, all at once. Now all values are really high and you can relax. But in your system the super high levels of calcium and carbonate combined with the even higher pH and even less magnesium has turned your reef into a crystal growing factory. A few days later things aren't looking so good so you break out the test kits again and... Hey! What the *@!*@ is going on? Also, as if things couldn't get more complicated, you are finally noticing the formation of "chalk" deposits on your pumps, in your plumbing and in between the grains of your aragonite substrate (clumping). It is time to take to heart a few simple rules that you may have forgotten along the way of your reef-keeping odyssey.

Sea water values of pH and ionic concentration are the stable equilibrium values in the wild and in your aquarium. Strive to maintain these values rather than significantly exceeding them. Pushing these values tends to give you an effect opposite of what is intended. Remember that one quality that all the famous reef-keepers possess is patience.

One of the most effective ways of keeping your system on an even keel is through regular partial water changes with a good quality salt mix. This will keep the water within certain acceptable parameters. This is good advice even when the water looks very clean.

Never exceed manufacturers recommended doses and keep in mind that dosing with similar products may give you cumulative amounts of certain compounds or elements.

Now to put your system right. First back down slowly on the kalkwasser use until your pH is back between 8.2 and 8.3 or until you notice a negative effect on aquarium inhabitants. You may well find that it is not needed at all to maintain calcium and carbonate levels, but that alone is not a good enough reason to discontinue the use of kalkwasser. The hydroxyl ion (of which you get two for every one calcium ion in kalkwasser) plays a major role in the neutralization of dissolved CO2 which is the primary factor for proper fish and invertebrate respiration (not oxygen!). Remember that low pH kills marine life by an increase in carbon dioxide solubility that leads to an inability of an animal to diffuse metabolic CO2 out of its tissues. Poorly circulated aquariums or large systems, may have CO2 accumulation rates that require kalkwasser to deal with. This is why you observe your animals. They will show you if they are suffocating. Also, if you find that your aquarium cannot run without kalkwasser get a dosing system now. If your pH is low, use a buffer and keep using it to bring it back into range (don't use kalkwasser to control pH!). Use calcium chloride to adjust calcium until it is in the normal range. And finally, sit back a bit and let the aragonite substrate do its job! Since the equilibrium pH value of aragonite is the same as sea water, it reacts on demand to supply pH and mineral support to a system. All the additives we have mentioned depress the chemical performance of aragonite substrates as they interfere with this aragonite/sea water equilibrium. Use Kalkwasser to control CO2 if you must, and use other additives to make slight adjustments to the water chemistry. If you are encountering chronic problems with your system look for a cure rather than masking the symptoms. It may mean changing or intensifying your circulation pattern, or pedestaling your live rock to avoid detritus accumulation. Many times opening up a tight fitting hood to enhance CO2 degassing, or even a circulating fan over the sump can have a lasting effect on the quality and stability of a system! You may just find that keeping your reef healthy means putting in less effort, not more.

Richard M. Greenfield Jr.

Marine Geologist

V.P. CaribSea inc.