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Old 02-24-2012, 08:18 PM
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Default Original Article by Troy Brightbill - Part 2

Correcting Magnesium Levels


The amount of magnesium precipitation that occurs in reef aquariums is very small compared to calcification rates. However, without periodic monitoring, the level can drop. In some cases, people have discovered they have drastically low magnesium levels, possibly a result of bad artificial saltwater mix. In light of this, Dallas Warren asked me to include some data on correcting magnesium deficiencies.

An initial concentration of 600mg/L was chosen. In natural saltwater, magnesium is found at roughly three times the concentration of calcium. A target level of 1200mg/L has been selected. Using the graph in Figure 5 , one can find how many weeks it takes to reach 1200mg/L using water changes, for any tank size. Using 25% or 50% changes, you will see that the graph begins to plateau as the magnesium level nears 1200mg/L. The same occurs as the levels approach 1200mg/L using 10% water changes. Yet with 25 weeks of performing a 10% change per week, the magnesium level is still not up to 1200mg/L. It would take 16 water changes at 10% water volume to reach even 1100mg/L. Using 25% changes, it would take 6 changes to reach 1100mg/L, and about 18 changes to finally reach 1200mg/L. Using 50% water changes - which by most accounts are stressful on reef tank inhabitants - would take 3 changes to clear 1100mg/L, and about 12 changes to reach 1200mg/L. Notice the large number of changes, for all 3 percentages shown here, required just to go from 1100mg/L to 1200mg/L. Notice also that water changes are by no means fast nor inexpensive when used to correct such ionic imbalances.


The most common method used by reef aquarists to replenish magnesium is the use of... drum roll, please.... Epsom salts. Epsom salt is simply hydrous magnesium sulfate, with a molecular formula of MgSO 4 -7H 2 O. Magnesium makes up 10.5% of Epsom salts by mass. To replenish 600mg/L in the 55 gallon tank used in this example, 90.8 grams of magnesium is required. This requires 898.1g of Epsom salts. I would recommend dividing this amount up to be dosed over a period of atleast one week, if not more. A 25% to 50% initial water change will reduce the amount required significantly, but after the first water change, each subsequent water change becomes increasingly less effective.
Hydrous magnesium sulfate will increase the sulfate concentration in the saltwater along with the magnesium concentration. Unfortunately, most aquarists don't have the means to test their sulfate levels. Again, an initial water change will help alleviate this problem somewhat. Another option would be Magnesium Chloride, but it is not as easy to find, and could eventually raise Cl - levels. More on dosing Epsom salts can be read at Dallas Warren's website (look in the DIY section).
Trace Elements

Recent works have shown that the artificial saltwater mixes on the market today contain higher trace element levels than those found in natural saltwater. Protein skimming and use of carbon are suspected to remove trace elements to some extent, but there is currently no method of measuring the level of trace elements readily available to reef aquarists. One would expect the reef animals to make use of these trace elements as well. Therefore, some method of replenishing these levels must be implemented in our reef aquariums.
Considering that artificial saltwater mix contains elevated levels of trace elements (Atkinson, data presented at WMC 1998), one can rely solely on water changes to replenish them because the initial levels from the salt mix are higher than the levels found in natural saltwater. While I do not have the actual data on hand (I'm trying to track it down at the moment), I believe that even a single 10% water change in a month can account for any loss of trace elements in the system. Many have proposed dosing trace element supplements at as little as one half to one tenth of the prescribed dosage to maintain trace element levels. In my opinion, trace element replenishment is not a major issue when considering whether or not to conduct frequent water changes. For those truly concerned, a $10-20 bottle of trace elements supplement will last you a very long time, costing even less per day than the kalkwasser.
Summary


The intent of this article is not to scare people out of conducting frequent water changes, nor to single out those who propose conducting frequent water changes. By frequent, I mean 2-4 water changes per month. The intent of this article was to debunk the common myths as to why people need to conduct frequent water changes of 10-25% nominal water volume. Through basic chemical equations, I have attempted to show how long it actually takes to correct elevated nutrient levels in our reef aquariums. Water changes on the order of 10% to 25% nominal volume, when carried out on a weekly basis, have been shown to be a very slow method for lowering nutrient levels. A larger initial change of 50% nominal volume will be far more effective, but this usually causes a great deal of stress for the aquarium inhabitants. I have also attempted to show how water changes alone will not compensate for calcium consumption. It is a basic mathematical relationship - since the salt mix only supplies these chemicals at levels near natural saltwater levels, it will not make up for uptake of these chemicals when partial water volume changes are performed. The only true way to have water changes alone maintain the saltwater chemistry is to have a truely open system, such as at Wakiki Aquarium.
Frequent water changes, when performed correctly, will not cause any noticeable harm to your aquarium. Water changes are required to correct Cl - ionic imbalances, usually resulting from the frequent use of calcium chloride (CaCl 2 ), as nothing will physically remove Cl - alone from the water without ripping out every other anion. I feel that water changes are most beneficial when used to remove particulate wastes from the substrate of the aquarium, when cleaning plumbing, and when cleaning the protein skimmer. I prefer to do a monthly water change to perform these tasks.
Conclusion

Weekly water changes will not maintain calcium levels in a reef aquarium. Some form of additional input, such as calcium hydroxide, is needed to maintain the calcium level. It can take months to correct nutrient levels with water changes alone. This isn't anecdotal evidence, this is clearly displayed in the previous calculations. I feel strongly that a properly run reef aquarium - utilizing protein skimming, calcium hydroxide dosing, dosing of potassium iodide and other essential trace elements, and a monthly cleaning requiring about a 10% water change - will thrive. Other than these simple requirements, there are numerous methods people can use.
It is better to maintain the levels discussed here, rather than have them swing up and down on a weekly basis. This is a common effect resulting from frequent water changes. In the preceding text I have questioned the actual need for frequent water changes, and I have attempted to dispel many of the myths about why people need to perform them, as well as myths about what they accomplish.
For further data and graphs (Figures 1-5), see t_brightbill_wcdata.html .
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