Alkalinity: After losing almost all my live stock in the last week, I did some major reading and research on one water parameter that I feel most beginners negligent, that is kH. It all started when I failed to test kH and started to witness how my tank is moving backwards, Fish becoming sick/stressed and corals not opening, tube worms no coming out... kH/Carbonate Hardness works inline with Calcium, One thing I could not understand in the last 2 weeks, why is my Calcium sky high climbing through the ceiling... Only to find out that my kH is on 3 ... So after consulting everyone on MASA I started to dose baking soda/bicarbonate of soda. I managed to get my Calcium down and my kH back on 7.5, only to find out this was too late due to kH not being right, all my life stock started to stress and all my tangs starting to get WHITE SPOTS, and eventually velvet disease and very aggressive bacterial infections... I managed to QT my only tang that is still surviving, my Sailfin tang, currently treating him with copper, but my hopes is low on survival... almost all his fins is gone due to the bacterial infection, but somehow he is still alive. I found an interesting article, feel free to co rectify me if I`m wrong and please all moderators share with us some experience and advice. Alkalinity: Understanding Reef Tank water Testing and Parameters What is it? (Related to pH) Scientifically, alkalinity is a measure of the acid neutralizing capacity of a solution. I know…a bit wordy, right? But in regards to the marine aquarist, it's simply the measure of the ability of your tank's water to hold its current pH levels as well as a measure of the amount of calcium carbonate (used in the process of building skeletal mass). The better your alkalinity value, the less likely you are to have pH swings. Alkalinity is also tightly relates to Calcium levels, but we'll get into that later. In the marine hobby, this value is almost always measured in terms of Carbonate Hardness, or KH (not to be confused with general hardness GH, which is the value usually tested for in the Freshwater hobby). Why's it Important? Alkalinity's affect on the tank is a big one, but is rather indirect. As mentioned before, it's mainly a measure of Calcium Carbonate, but without getting advanced, it's also a measure of the tank's ability to maintain its pH levels. So indirectly, if your alkalinity is off, then all the affects that pH has on the system come in to play. Bad alkalinity can allow rapidly shifting pH values which in turn will cause bad chemical reactions to take place in the tank. Alkalinity is also very tightly related to calcification. Calcification really requires a scientific explanation to truly understand it, which is why I include a lot of links going into detail on this subject later on. But in staying with the goal of THIS article, I think it's easiest to also think of it as the ability of the tank's water to hold calcium as well as the critters abilities to utilize that calcium in the water column. Once the tank's water is super-saturated, Alkalinity and Calcium levels become inversely related. Raising alkalinity can cause Calcium levels to drop, and raising Calcium levels can cause alkalinity to drop. Let me explain this with an analogy. Let's say you have a normal sized shoebox and let's say you an unlimited supply of red golf Balls and an unlimited supply of blue golf balls. You can only fit some finite number of golf balls in the shoe box, regardless of their color. Initially you can have a few red golf balls and way more blue ones. Then you could add lots of red ones to make the amount more even. You can keep adding various colored balls until eventually, the shoebox will be full. This is when the box has reached super-saturation (fancy word for, "it's all full"!) Take note that until the box fills up though, there is no correlation between the red and blue golf balls, meaning that adding a blue ball does not affect the number of red balls in the box. But once the box is full (super-saturated), in order to increase the number of blue balls in the box, you are going to have to remove a red ball. This is what happens with Calcium and Alkalinity in your tank's water column. The water can only hold so much dissolved stuff over all. Once it's full, putting one in the water column can force the other out (precipitation). At balanced super-saturated levels, corals can more easily pull the calcium they need from the water column, and as a result, can potentially grow faster. However, if the super-saturated line is crossed, precipitation can occur in the tank. This is a fine line to balance when trying to achieve optimal growth rates, and is only suggest for an advanced hobbyist. Achieving super-saturation is not necessary, and as long as Alkalinity and Calcium levels are in an acceptable range, growth will not be inhibited. What Value should I Aim For? Anything from 2.5-4 meq/L (7-11 dKh) is acceptable. Actually there is no exact target you should shoot for, until you get more advanced. For the most part, as long as you're in that range, you are providing a good environment for your tank's critters. Higher alkalinity values than that range, and you can run into problems with precipitation. Basically, this means your water can not hold anymore calcium carbonate (main compound that an alkalinity value is measuring). So, as a result, excess calcium carbonate starts to solidify (much like when you put too much sugar in your iced tea). This excess will begin to accumulate on equipment, forming a crust or shell. This reaction is easier in warmer areas, so it's very common for things like heaters and pump impellers to get a build up on them. In extreme cases, you can even get what appears to be snow in the tank's water column. Lower values will cause instability in your tank's pH level. This may result in constantly lower or higher pH readings. Or even worse, wild swings in the tank's pH. This causes stress on all tank inhabitants leading to a slow demise, disease, and eventually death. What Do the Values mean? mEq/L - means milli-Equivalents per liter. dKh - means degrees of Carbonate hardness, and is simply 2.8 times the mEq/L value. Both of these are chemistry terms which to truly explain them would require chemical explanations that are more advanced than the purpose of this article. I've included links that go into more detail about each later in this section, but for now, let's just think of them as units of measure for alkalinity. When Should I Test For It? Whenever your having problems with or trying to maintain your tank's pH, Alkalinity, or Calcium levels. If you're trying to keep calcifying corals (corals with a skeleton) and are trying to maintain good growth conditions, testing for alkalinity is a must. Anytime you are dosing in any fashion in an attempt to affect pH, Alkalinity, Calcium, Magnesium, Strontium, etc levels, monitoring your Alkalinity levels is highly suggested. At least until you become familiar with it's affect on your tank.