KH is killing me!

Dear Seagazer:

Yup, your carbonate hardness or KH is definitely running a bit high right now. If you are adding a pH buffer or supplementing your reef tank with calcium, that may be contributing to the problem and I would discontinue such buffers or additives until your KH comes back down to normal levels. That should only be a matter of time since the live corals and calcareous algae in your reef system are actively removing bicarbonate from the aquarium water for metabolism and growth, reducing the carbonate hardness in the process. Water changes using unbuffered RO/DI softened water will also help bring the KH down, but I would wait a bit before I performed another partial water change.

Here are some excerpts from my new book (Complete Guide to the Greater Seahorses) that discuss the relationship between pH, buffers, alkalinity, carbonate hardness (KH) and calcium in greater detail:

pH: Optimum level = 8.1 – 8.4 (typically fluctuates between 7.9 at night and 8.4 during the day)

The pH is a measurement of the alkalinity or acidity of aquarium water. A pH of 7 is considered to be "neutral," neither acid or alkaline, while pH levels above 7 are considered to be alkaline or "base," and pH levels below 7 are considered to be acidic. Marine aquaria need to maintain alkaline conditions at all times, and low pH (< 7.6) is especially detrimental to seahorses because it is conducive to Gas Bubble Disease. Normal daily fluctuations in pH are to be expected in the aquarium, and are generally gradual enough not to be stressful (Webber, 2004). Maintaining a sump with a reverse photoperiod to the main tank can eliminate these natural pH cycles. Regular partial water changes are the key to maintaining stable pH. Buffers can also help but the hobbyist should beware that excessive use of pH buffers may increase KH values to dangerously high levels.

Alkalinity: Optimum level = 2.4 milliequivalents per litre (meq/L), which is the alkalinity of natural seawater, is best for fish tanks; > 3.0 meq/L is recommend for reef tanks.

The alkalinity is basically a measure of the capability of your aquarium water to resist changes in pH from the addition of acid (Trevor-Jones, Nov. 2002). Acid is continually entering the aquarium, primarily as the result of respiration (CO2) and metabolic wastes produced by the aquarium inhabitants (Trevor-Jones, Nov. 2002). The addition of these acids tends to lower the pH of the aquarium water. The higher the alkalinity of your aquarium water, the more resistant it is to such downward pH shifts (Trevor-Jones, Nov. 2002). The amount of buffers (primarily carbonate and bicarbonate) in saltwater determines the alkalinity, so the alkalinity in effect is the buffering capacity (Trevor-Jones, Nov. 2002). When the buffering capacity of the water is depleted, the pH becomes unstable. Alkalinity test kits can now warn of low buffering levels in time to prevent potential pH problems (Trevor-Jones, Nov. 2002).

Carbonate Hardness (KH): Optimum level = 7dKH (the hardness of natural seawater)

Carbonate hardness is another measurement of alkalinity. It is usually expressed in the German unit dKH (degrees of carbonate hardness) and is often considered to be the total alkalinity. (Dividing dKH by 2.8 will give you the alkalinity in meq/L.) KH is actually a measurement of various carbonates and bicarbonates of calcium and magnesium within the aquarium water (Webber, 2004). Maintaining a stable KH is very desirable since it maintains the buffering capacity (i.e., alkalinity) of the system and prevents subsequent drops in pH. Aside from stabilizing the pH, reef keepers need to maintain KH and high alkalinity in order to assure that the calcifying organisms in the tank flourish. Corals and other calcifying organisms actively use bicarbonate, which is the main component of alkalinity, so the alkalinity of a tank with a lot of calcification can drop quite rapidly.

Calcium (Ca): Optimum level = 350 – 400 ppm (up to 500 ppm in well-stocked reef tanks)

Calcium is a very important element in the water in any marine aquarium and is a vital element in reef tanks. Along with carbonates and bicarbonates, it is required by calcifying organisms such as stony corals, snails and other mollusks, coralline, Halimeda and other calcareous algae, and certain sponges (Trevor-Jones, Apr. 2003). Calcium reserves must therefore be replenished on a regular basis. Regular water changes may achieve this, but reef keepers may require the addition of biologically available calcium to maintain adequate levels (Trevor-Jones, Apr. 2003). Seahorse keepers should be aware that brooding males provide calcium to the developing fry in their pouches, which the embryos probably incorporate into their skeletons. Deficiencies in calcium could thus adversely affect your seahorses’ reproductive success and the health of the fry. In fact, seahorses that receive a diet deficient in calcium often suffer from decalcification of their exoskeleton, a debilitating condition commonly known as "soft plate" disease (Greco, 2004).

Best of luck with your reef system, Seagazer!

Respectfully,
Pete Giwojna

Dear Seagazer:

Yes, offhand I know of no products designed to lower KH in a marine aquarium, nor am I aware of any products intended to absorb carbonates from saltwater.

So for the time being, I would just ignore the fact that your pH and calcium levels are running a a little low. Avoid adding any pH buffers or calcium supplements (including Sea Balance) for the time being, and your high carbonate hardness or KH levels will gradually come down as the calcifying organisms in the aquarium remove carbonates from the water. How quickly that happens depends on the number of calcifying organisms in the aquarium (e.g., live corals, coralline algae, calcareous algae such as Halimeda, various mollusks and crustaceans) and how high your KH has risen. For example, the carbonate levels will come down much more quickly in a reef tank with lots of live coral, gorgonia and Tridacna clams than they will in your average seahorse tank. And they will drop faster in a seahorse tank with mushrooms and other soft corals, coralline algae, and Halimeda macroalgae than in a seahorse-only setup that just has a cleanup crew with snails, micro-hermit crabs, and perhaps a few cleaner shrimp.

Once your carbonate hardness or KH has come back down to the normal range, Seagazer, you can then address your low pH and calcium levels. In my experience, the best way to stabilize your pH at the proper level is to gradually adjust it upwards as usual, and then use a 2-part Calcium Buffer System periodically thereafter.

To adjust your pH to the proper range (8.1-8.4) initially, just obtain one of the commercially made products designed to adjust the pH upwards in saltwater aquariums and use it according to the instructions. Such a product should be available from any good LFS that handles marine fishes and invertebrates; they typically include sodium bicarbonate as their primary active ingredient and are often marketed under names such as "pH Up" or something similar. Just be patient when you are adjusting the pH and don’t add too much of the product too soon. Very often your pH won’t budge at all the first several times that you add the product according to directions. That’s perfectly normal, so don’t be discouraged if your pH stays at 7.8 even though you’ve added several doses of the product you obtained to raise the pH. Don’t don’t be tempted to add more of it or to add it more often than specified in the instructions. The product must first overcome the natural buffering ability of the saltwater in your aquarium before I can change the pH level significantly. Typically, you add several doses and your pH doesn’t budge at all, but then the very next dose you add may change the pH dramatically. Since you never know when that critical point will be reached, remain patient and continue to carefully add more of the product as directed until the pH does start to change, and then adjust it to the desired level as gradually as possible.

Once the pH has been adjusted to the proper level, you then add the alkalinity component of the 2-part buffer system. Next you wait a couple of minutes and add the calcium component of the 2-part buffer system. Your pH should remain stable at that pH thereafter and this method also has the added benefit of keeping your calcium level in the proper range as well. For a typical seahorse tank, you can keep it stable at the desired pH by adding more of the 2-part Calcium Buffer System about once a week after your water changes.

The 2-Part Calcium Buffer System that Marcie and some of our other members report works well with their seahorse tanks is labeled "ESV B-Ionic" on the bottles, but it sounds like the Sea Balance you have been using does much the same thing. The alkalinity component of these two-part buffers maintains the carbonate hardness or KH in the aquarium, whereas the calcium component maintains the calcium levels in the proper range.

In short, time should gradually solve your problem with excessively high KH, and once your carbonate hardness levels are back to normal, you should then be able to correct your pH in calcium levels as described above. For best results, I would discontinue the Kent buffer and stick with a 2-part Calcium Buffer System such as we have been discussing instead.

You might also consider posting this question on the Seahorse and Pipefish Forum at reefCentral.com, since reefkeepers must monitor and adjust their carbonate hardness much more carefully than us seahorse keepers. The guys at reefcentral may well know some tricks or techniques for adjusting KH that I am unaware of…

Best wishes with all your fishes, Seagazer!

Respectfully,
Pete Giwojna