TDS/Mineral Requirements

Dear Diane:

You wrote:

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What is the preferred TDS (total dissolved solids) level for seahorses? And more specifically, how many ppm of calcium and magnesium are ideal for them?

I take great care to provide ideal Ca/Mg/TDS levels for my goldfish, and I want to do the same when I get my seahorses. For the goldies, I start by filtering my softened well water through an RO unit. As it is filtered, the RO water trickles through a homemade degassing column to remove microbubbles. Then I mix the RO water 50/50 with our unsoftened well water. This achieves an ideal carbonate level and puts back some calcium and magnesium. (The unadultered well water is way TOO high in carbonates, and of course, the pure softened water has no minerals at all.) Finally I add additional calcium, magnesium, and trace elements to achieve ideal levels. I check TDS levels weekly with a TDS meter, and monthly I check Ca/Mg levels with a Ca/Mg photometer. Since I started doing this, none of my fish have had problems with swim bladder disease or fluid buildup. (In the past, I lost a few that way.)

Can high-quality marine salt mixes provide levels of calcium and magnesium ideal for seahorses? Or should I adjust them as I do for my goldfish? Which salt mix do you recommend?

Thanks!

Regards,
Diane

http://www.freshwaterpearlspuppetry.com/bubbleblog/
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With a fish-only saltwater aquarium, Diane, the artificial salt mix will generally include the proper amount of calcium, magnesium, and other minerals. As long as you maintain the pH in the proper range, further supplementation with calcium and magnesium is normally not needed in a fish-only marine aquarium. Good old Instant Ocean will suffice for such a setup; it’s not generally necessary to invest in the more expensive salt mixes for a tank that will house only fish and a cleanup crew.

Most marine aquarists like to start out with RO/DI water that is ultrapure, add the appropriate amount of artificial salt mix for the volume of saltwater they are preparing, and then add a good aquarium buffer if necessary to achieve the desired pH. In most instances, the home hobbyist need only concern himself with monitoring the basic aquarium parameters (water temperature, salinity or specific gravity, pH, and the levels of ammonia, nitrite, and nitrate) for a fish-only aquarium system.

However, reef keepers and seahorse keepers that will be maintaining seahorse-safe corals with their ponies will often monitor a long list of other aquarium parameters, including the levels of calcium and magnesium. Supplementation with calcium is often necessary for such systems because the calcifying organisms (live corals, calcareous macroalgae, coralline algae, snails, various crustaceans, etc.) can rapidly deplete the amount of bioavailable calcium. So in reef systems and seahorse tanks that include live corals, the appropriate amounts of calcium and magnesium to maintain are as follows:

Calcium (Ca):
Natural Seawater Value = 400 mg/L
Acceptable Range = 350 to 450 mg/L
Optimum Level = 350 – 400 mg/L (up to 500 mg/L 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 is a critical parameter for coral growth in reef aquariums, and chronically low levels will cause coral mortality and loss of coralline algae and other invertebrate species. 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).

Magnesium (Mg):
Natural Seawater Value = 1280 mg/L
Acceptable Range = 1100 to 1400 mg/L
Optimum Level = ~1280 mg/L

Magnesium is a key component of the water buffering system, and is incorporated into coral skeletons as the corals grow. It also plays a vital role in all photosynthetic processes. Low levels of magnesium indicate the need for more frequent partial water changes and/or buffering of the aquarium.

However, Diane, when supplementing the calcium and/or magnesium, it is not sufficient merely to monitor the calcium levels and magnesium levels in the aquarium. Rather, it is also important to monitor the total alkalinity and carbonate hardness in the aquarium as well, in order to assure that all of the levels remain at the proper balance and that the pH of the water is always within the proper range:

Alkalinity:
Natural Seawater Value = 2.5 meq/L
Acceptable Range = 2.5 to 5.0 meq/L
Optimum Level = 2.5 milliequivalents per litre (meq/L)is best for fish tanks; > 3.0 meq/L but < 5.0 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. A fluctuating alkalinity will lead to serious problems in
maintaining an appropriate pH, as well as problems keeping calcium and magnesium levels within required ranges. Alkalinity test kits can now warn of low buffering levels in time to prevent potential pH problems (Trevor-Jones, Nov. 2002).

Carbonate Hardness (KH):
Natural Seawater Value = 7 dKH
Optimum Level = 7dKH (for seahorses)

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. For this reason, although 7dKH is excellent for a seahorse only setup, or a tank with seahorses and a few hand-picked soft corals, aquariums with stony corals, calcareous macroalgae, or a lot of coralline algae can benefit from a somewhat higher KH reading. A good brand of artificial sea salt for a reef tank will yield a KH between 8-12 after being freshly mixed, in order to allow for the calcification that will occur once the water change is made. 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. However, you do not want the KH in the aquarium to rise above 13dKH for any length of time since KH readings in the 14-15 range and above can cause calcium to begin to precipitate out of the water, making it increasingly difficult to maintain an adequate calcium level in the aquarium…

In short, Diane, as long as you will be maintaining a fish-only saltwater aquarium, you will most likely not need to be concerned about the calcium and magnesium levels, since performing regular partial water changes will suffice to maintain them at adequate levels. But when you begin adding supplements, then it’s important to monitor a whole galaxy of water quality parameters to make sure that everything remains in balance. The proper levels for the various minerals and trace elements in reef tanks or seahorse tanks that include live corals are explained in detail in Lesson 4 of the seahorse training program, which you will be receiving in a few days…

Likewise, most marine aquarists with fish-only systems do not concern themselves with the total dissolved solids in the aquarium. Many hobbyists only monitor them to determine if their RO/DI unit is working properly, since a rise in the TDS can indicate that the membranes need to be replaced.

Best wishes with all your fishes, Diane!

Respectfully,
Pete Giwojna