Water Chemistry - A simplified Analysis by Kirk Masters aka Kaptnk, Amazing Coral Reef
Areas covered: - Chloride Buildup
Sea water typically has a pH of 8.2. The dKH is around 7 and the calcium level is 380-400 ppm and sometimes higher around coral reefs. The strontium levels are 8-10 ppm. The volume of water is massive compared to the volume or area of reef rook. The biological activity is immense, with 10's of thousands of tiny life forms in sand and rocks in each ml of sand!.
In our aquariums the opposite is true. We have a lot of rock and a little water. Changes or consumption of the water chemistry occurs rapidly and depletion can stop all growth and lead to death if not corrected.
How do we make things works then in a Reef?
We make up the calcium and alkalinity losses by using calcium hydroxide in our makeup water. We add extra calcium as calcium chloride and strontium as Strontium Chloride. The natural carbon dioxide in the water converts to bicarbonate ion and we get Strontium bicarbonate and Calcium bicarbonate with the chlorides finding another mate or reacting with water. Every time you add CaOH it will react with chlorides to give CaCl, thus neutralizing the Chlorides. This leads us to the Calcium bank but first let us review soluability.
This looks at how much calcium and how much strontium we can keep in the water. Factors affecting this are the salinaty of the water, pH and other competing ions. Very little is published on strontium but it has similar physical properties to calcium as it is in the same family only bigger. You can not expect to maintain the same ion level at a salinity of 1.020 verse 1.024(best). If you have increased the strontium level to 20-30 ppm it will affect the maxium amount of calcium you can keep in the water. Also operating at a higher pH will lower the amount of calcium you can keep in the water. This does not hurt anything but is important to know when you find out that you can not increase your calcium to greater than say 525 ppm. at a pH of 8.4, strontium of about 30 ppm and salinity of 1.024. The readings you get on your test kit must be compared to a standard as the EDTA tiration solution
giving you a false high reading. The Amazing Coral Reef's Calcium test kit comes with a standard solution and is twice as sensitive as other test kits.
When we measure the calcium ion level in a reef we measure all of the calcium. The form of the calcium will be in the chloride, sulphate or bicarbonate form. Corals, coralline algae use the bicarbonate form for most of their needs. Example: If you have 400 ppm Ca as the ion you have 1000 ppm as CaCO3. If your dKH is 10 you have 171 ppm bicarbonate alkalinity expressed as CaCO3. You can now see that most of you calcium is a reserve waiting to be changed to bicarbonate ion. If you have 30 ppm strontium also, then the strontium is all in the bicarbonate form and the remaining bicarbonate is in the calcium form.
We add SrCl and CaCl to our Reefs. This wants to change to the bicarbonate form. If some of the chloride can not find a mate (cation) it will grab H+ from the water and form an acid. Our CaOH will neutralize this and form CaCl. This bulid up of chlorides can keep our pH from getting above 8.25 or reaching the optimum level of 8.3 to 8.4.(Maximum calcification occurs at a pH of 8.4 ie. maximum coralline algae and stoney coral growth occurs at a pH of 8.4). The solution is very simple. We must add sodium to match the Chloride level. Most of the buffers you see on the market are diluted. Amazing Coral Reef uses pure buffer ( KH Builder) . By adding one level unit of KH Builder to one level unit of CaCl , the resulting product is Calcium in bicarbonate form and salt (NaCl). This will not increace your salt level noticably.(If used for all of your Calcium needs it will increase your salt level by 0.004% per day. Therefore use a 10% water change per month or more like 5% per week gives great results) It will also help to keep your pH high were you want it to be. The same thing happens with our Strontium Chloride and we need to add a much smaller amount to form salt. The use of a pH meter will very quickly show you your correct operating range and when your pH begins to fall you can add the KH Builder to correct the situation.
We recommend that Kalkwasser be used to keep your Calcium level up on a daily basis and that you only use Calcium Chloride as a means to off set any difficulties you might have with Kalkwasser. Be aware of low magnesium levels which prevent your calcium from reaching normal levels. We have long suspected that Kalkwasser could cause some magnesium to be lost from the system and this appears so.
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