View Single Post
Old 23-09-2007, 10:16 PM   #4
valerossi
Arofanatic
 
valerossi's Avatar
 
Join Date: Feb 2005
Posts: 348
Default

Iodine

I do not presently dose iodine to my aquarium, and do not recommend that others necessarily do so either. Iodine dosing is much more complicated than dosing other ions due to its substantial number of different naturally existing forms, the number of different forms that aquarists actually dose, the fact that all of these forms can interconvert in reef aquaria, and the fact that the available test kits detect only a subset of the total forms present. This complexity, coupled with the fact that no commonly kept reef aquarium species are known to require significant iodine, suggests that dosing is unnecessary and problematic.

For these reasons, I advise aquarists to NOT try to maintain a specific iodine concentration using supplementation and test kits.

Iodine in the ocean exists in a wide variety of forms, both organic and inorganic, and the iodine cycles between these various compounds are very complex and are still an area of active research. The nature of inorganic iodine in the oceans has been generally known for decades. The two predominate forms are iodate (IO3-) and iodide (I-). Together these two iodine species usually add up to about 0.06 ppm total iodine, but the reported values vary by a factor of about two. In surface seawater, iodate usually dominates, with typical values in the range of 0.04 to 0.06 ppm iodine. Likewise, iodide is usually present at lower concentrations, typically 0.01 to 0.02 ppm iodine.

Organic forms of iodine are any in which the iodine atom is covalently attached to a carbon atom, such as methyl iodide, CH3I. The concentrations of these organic forms (of which there are many different molecules) are only now becoming recognized by oceanographers. In some coastal areas, organic forms can comprise up to 40% of the total iodine, so many previous reports of negligible levels of organoiodine compounds may be incorrect.

The primary organisms in reef aquaria that "use" iodine, at least as far as are known in the scientific literature, are algae (both micro and macro). My experiments with Caulerpa racemosa and Chaetomorpha sp. suggest that iodide additions do not increase the growth rate of these macroalgae, which are commonly used in refugia.

Finally, for those interested in dosing iodine, I suggest that iodide is the most appropriate form for dosing. Iodide is more readily used by some organisms than is iodate, and it is detected by both currently available iodine test kits (Seachem and Salifert).

Nitrate

Nitrate is an ion that has long dogged aquarists. The nitrogen that forms it comes in with foods, and can, in many aquaria, raise nitrate enough to make it difficult to maintain natural levels. A decade or two ago, many aquarists performed water changes with nitrate reduction as one of their primary goals. Fortunately, we now have a large array of ways to keep nitrate in check, and modern aquaria suffer far less from elevated nitrate than did those in the past.

Nitrate is often associated with algae, and indeed the growth of algae is often spurred by excess nutrients, including nitrate. Other potential aquarium pests, such as dinoflagellates, are also spurred by excess nitrate and other nutrients. Nitrate itself is not particularly toxic at the levels usually found in aquaria, at least as is so far known in the scientific literature. Nevertheless, elevated nitrate levels can excessively spur the growth of zooxanthellae, which in turn can actually decrease the growth rate of their host coral.

For these reasons, most reef aquarists strive to keep nitrate levels down. A good target is less than 0.2 ppm nitrate. Reef aquaria can function acceptably at much higher nitrate levels (say, 20 ppm), but run greater risks of the problems described above.

There are many ways to reduce nitrate, including reducing the aquarium's nitrogen inputs, increasing nitrogen export by skimming, increasing nitrogen export by growing and harvesting macroalgae or turf algae (or any other organism of your choice), using a deep sand bed, removing existing filters designed to facilitate the nitrogen cycle, using a carbon denitrator, using a sulfur denitrator, using AZ-NO3, using nitrate absorbing solids, and using polymers and carbon that bind organics. All of these methods are described in more detail in a previous article.

Nitrite

Aquarists' concerns about nitrite are usually imported from the freshwater hobby. Nitrite is far less toxic in seawater than in freshwater. Fish are typically able to survive in seawater with more than 100 ppm nitrite!17 Until future experiments show substantial nitrite toxicity to reef aquarium inhabitants, nitrite is not an important parameter for reef aquarists to monitor. Tracking nitrite in a new reef aquarium can nevertheless be instructive by showing the biochemical processes that are taking place. In most cases, I do not recommend that aquarists bother to measure nitrite in established aquaria.

Strontium

My recommendation is to maintain strontium levels in reef aquaria in the range of 5-15 ppm. That level roughly spans the level in natural seawater of 8 ppm. I do not recommend that aquarists supplement strontium unless they have measured strontium and found it to be depleted to below 5 ppm. Measuring and supplementing strontium is not a critical activity for most aquarists, and is not a trivial exercise since the available test kits can be difficult to use (see below).

In some recent tests, I found that in my reef aquarium, without any recent strontium additions, strontium was already elevated above natural levels (to 15 ppm due to elevated strontium in the Instant Ocean salt mix that I was using). I would not like to see it get any higher. Consequently, adding a supplement without knowing the aquarium's current strontium level is not advisable. Scientific evidence indicates that some organisms need strontium, albeit not the organisms that most reef keepers maintain. Certain gastropods, cephalopods, and radiolaria, for example, require strontium.18-34 It is, however, clearly toxic at elevated concentrations. In one reported case, 38 ppm was enough strontium to kill a particular species of crab (Carcinus maenas).34 No evidence indicates that 5-15 ppm strontium is harmful to any marine organism, although it is not known what strontium levels are optimal. Finally, anecdotal evidence from a number of advanced aquarists suggests that strontium that is substantially below natural levels is detrimental to the growth of corals that many aquarists maintain, but this effect has not been proven.

How can we maintain natural strontium levels? Doing so, of course, necessitates a suitable strontium test. Some test kits are perhaps suitable for this purpose. If not, sending a sample out to a lab might be a reasonable alternative for some aquarists. If the result comes back in the 5-15 ppm range, no action likely need be taken. If the level is higher than 15 ppm, the best reduction method may simply be water changes with a suitable salt mix, without abnormally high levels of strontium. If strontium levels are below 5 ppm, adding a strontium supplement may be in order.

Overall, water changes with a salt mix containing a suitable level of strontium may be the best way to keep strontium at appropriate levels.
valerossi is offline   Reply With Quote