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Iodine In The Reef aquarium |
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In this section I'll try to cover in simple terms this most complex of substances and try to offer offer some insight into its nature, uses, and drawbacks. In doing so I hope to dispel any myths or assumptions as to its use, but also possibly help cure an all too common phenomenon in SPS systems involving the slow and unexplained collapse of multiple colonies under conditions that 'apparently' show no adverse readings....So to kick off. What is Iodine..? Ah, now this is where I confuse many of you. You see 'iodine' as we know it, is not actually a 'single' chemical at all, and this is where most confusion arises. Many people dose various differing kinds without actually knowing 'what' they are dosing beyond the fact that marine additive manufacturers tell us it is essential for invert health, so should be dosed regularly. In fact many will claim that you will see vast improvements in livestock health when dosing 'Iodine'. You see, saying, or believing that dosing 'Iodine' is essential/beneficial, is like saying you like jam without expressing which kind you like, and without realising that there are many different 'kinds' of jam. Some tastier than others. Iodine in nature comes in many many differing forms (or species to be precise, which form into groups we could call families). two of which are relevant to what we are doing as far as dosing goes. the rest, all playing minor rolls and being largely uncontrollable as far as we are concerned, are still very obscure to the science world in terms of the rolls they play be it beneficial or otherwise. Plus these forms are not fixed. many can be converted by binding with other molecules under certain conditions or by biological action. The two main 'families' we look at are. Iodide. And Iodate. Iodide: Iodide concentrations in the ocean vary according to depth and possibly location. typically Iodide levels increase with depth. with a total average concentration in seawater of around 0.01-0.02ppm and is considered the 'biologically available' side of the coin. Iodate: On the other hand, normally 'decreases' in concentration at depth. but just like Iodide, can vary according to location. In the case of Iodate, average seawater concentrations are around 0.04-0.06ppm Typically, the combined 'total' Iodine concentration is around 0.06-0.08ppm Why is it important to know which one is relevant ?. Well the first myth to dispel is that commonly assumed one, 'Iodate is non-biologically available, whereas Iodide is' The truth of the matter is that 'both' fulfil important rolls in the biological function of a vast majority of marine life, from the largest fish, to the smallest bacteria and especially the algae's we use for nutrient control in reef aquaria such as Caulerpa or Cheatomorphyllia that can have a total body mass/iodine concentration of nearly 1% at 3/1 iodide to Iodate (doesn't sound allot, but it is). so neither should be dismissed offhandedly when discussing the need for iodine in both the forms we commonly encounter it. Many sponges Tunicates, and other organisms take up iodine as well, as a means to generate defensive chemicals that make the animal taste less appealing. in gorgonians increasing concentrations can be found with age. To be fair though, it is correct that in the vast majority of cases, the availability of 'Iodide' is our most important concern. What does Iodine do? Well that, is a complex question, and one with just as many unanswered aspects as there are answered ones. suffice to say, we do know that Iodine is essential for the proper functioning of cells and the transfer of nutrients within the cell structure. Likewise in larger organisms its essential for the proper functioning of the thyroid gland which releases hormones to control metabolism. In relation to Reef aquaria and corals, this would seem to fall in line with the theory that Iodine is essential for the creation of protective pigments within the cells to prevent UV damage, and the overall health of corals specifically relating to the cell structure and proper function at a cellular/nutrient level. It is also found at varying concentrations in the exoskeletons of crustaceans for which it is considered beneficial at the correct levels. Do I need to add Iodine..? Well, yet again there is a bit of a myth, in that it is 'claimed' that Iodine is depleted from aquaria extremely quickly by the use of powerful skimming, Carbon, or simply by assimilation. What isn't frequently considered is the fact that if you are feeding on a regular basis and doing regular water changes, the chances are in most cases, that your keeping up with demand quite admirably. Commercially available, and natural frozen foods contain more than enough to keep the vast majority of normally stocked systems happy. Its only in heavily stocked, or powerfully filtered Reef aquaria that problems with depletion 'may' be encountered or where water changes are infrequent. Sadly the advertising chat on the backs of most commercially available Iodine additives doesn't highlight this fact, and simply gives a weekly recommended dose aimed as a 'just in case' method of attack. This is one mentality most experienced reef-keepers would disagree with quite strongly. In essence, most experienced aquarists would always say 'don't add it unless you can test for it, and that goes for 'any' additive. The problem, is with the fact that iodine isn't a fixed 'single' element that can be measured easily like nitrate or nitrite etc... As already stated above, many forms are created and converted within the marine environment dependant on the system design and organisms present. so it doesn't take long to realise that there's no possible way to give a definitive guide to what should and shouldn't be present, baring in mind the hit and miss quality of many marine test kits when it comes to testing iodine. What's this about conversion of iodine types and what does it mean ? Remember that I said we can basically split our total iodine concentration down into two parts, Iodide, and Iodate. and that although commonly considered as more important, 'Iodide' is generally found at concentrations around 1/4 that of Iodate at natural levels. There are certain conditions, such as the anaerobic layers within sand beds and Live rock, where the absence of available O2, and a depletion in No3 cause bacteria to convert Iodate, into Iodide. This is a bit of a hodge -podge occurrence though, which doesn't seem to follow any specific trend that meets all scenarios. What does seem pretty consistent though, is that the conversion of Iodate to Iodide only seems to occur under conditions where nitrate is as low or as near to NSW as possible, and when Iodide is depleted below the normal NSW levels whilst Iodate remains high. Basically, this is of great benefit to us, especially those running DSB's compared to those running bare bottom systems. In such systems it is actually quite feasible (but rare) to see a total turn around in the balance between Iodate and Iodide levels, with iodide becoming the predominant species. Another pathway for conversion is via Phytoplankton. In libratory tests Phytoplankton were able to convert the entire concentration of available Iodate to Iodide quite quickly, so if your regularly feeding 'live' phyto, you have yet another pathway for the ongoing conversion of surplus Iodate, into freely available iodide. However the dosing of phyto solely for this purpose should be avoided as it can bring its own drawbacks if the source isn't very clean. So what does all this mean.? Well in simple terms it means that if you are running either a DSB or dosing live Phyto and have very low free levels of No3 (sub 0.1ppm) , then as long as your regularly doing water changes, and have a good healthy feeding regime, the chances of you suffering total Iodide depletion are quite slim. (accepting that your not running excessively high skimming capacity, large amounts of carbon or large amounts of macro algae). If your running at free No3 levels above NSW, (say 5.00ppm + ) then there 'is' the possibility that with large volumes of macro algae, heavy skimming and carbon use, even with a DSB or dosing Phyto, then you could look at Iodine as a worthwhile addition should your corals look a bit on the drab side or your looking at unexplained SPS problems. ( I'll get to this shortly ) remember this is because free Iodate isn't converted by DSB's under conditions of elevated No3 to the more beneficial form of iodide.. Ultimately you should let a 'test' dictate your actions. Iodine Test kits. There are several on the market available from differing manufacturers, but its important to note that whilst some such as Salifert give the 'total combined' iodine level, many only give either the Iodate, or Iodide reading. Personally, I prefer the Salifert one because it gives a better overall view and covers both species, so thereby ruling out excessive levels of one or the other un-noticed.. But be warned, Iodine test kits are a bit of a handful, with numerous different solutions to be added in various quantities in specific times before you get anywhere near a reliable reading, so patience, accuracy, and practice is essential if you want reliable results. One very important feature of iodine test kits is that you must cap the various liquids as soon as you've used them. Leaving the lids off, and exposing them to air is very detrimental to the long term accuracy of the kit. You've got a low reading (below 0.06ppm - 0.08ppm). well firstly don't panic. this isn't that uncommon. Allot of tanks will run under NSW levels of Iodine without too much problems. However, should you wish to increase levels, then you need to look for an ionically balanced additive that has iodide as a main constituent. Stick to the manufacturers dosage limits and test once per week to see how things are going. If you have seriously depleted levels or are suffering unexplained SPS losses*, then you may want to consider the alternate 'boosting' method I shall highlight below. * Unexplained SPS issues.: Over the last several years I and a few others have witnessed a regular phenomenon whereby previously healthy and well run tanks with seemingly perfect water conditions suddenly start to show a downturn in the health of SPS and other stony corals. The visual symptoms are pretty much standard across the board, i.e. an initial thinning of the tissue on the exposed tips and upper surfaces of the branches of Acropora's near the top of the tank. Which makes it look as though the tips have been 'nibbled' or 'bitten'. Quite often encroaching algae will immediately start growing on the tips giving rise to the common diagnosis that the algae are the problem or that there is a problem with the lamps. As things get worse this damage progresses with increasing loss of pigment, powdery tips, various degrees of tissue necrosis across exposed areas until the colonies finally collapse and die. Also affected are plating Montipora etc, which will pale off and start going soft at the growth edge. commonly the colonies will start loosing patches of tissue from the inner regions of the plates which gradually spreads out until the entire colony collapses. What's happening ? Well, personally, I feel that in cases where there is very strong skimming, large amounts of macro algae and slightly elevated N03 levels, then there is a distinct possibility that the system is suffering seasonal iodine suppression or depletion. Why seasonal?. Well most instances seem to occur in either late summer/autumn, or shortly after the spring. This would indicate some links to shifts in ambient temperature and the seasonal boost in macro algae growth encountered during summer months when the average daily temperature of the tank has shifted by a small degree. (NB: even with a good controller the average tank will shift in 24/7 temperature range by at least .5deg which is quite sufficient to trigger algae into seasonal growth patterns) its this increase in growth rate and the systems Iodine requirements that I feel is the main reason for the similarity in cases where Iodine depletion was found to be a major factor in the coral losses and condition. Add to this that in nearly all cases I've witnessed these symptoms have appeared across spring/summer autumn. I have never seen new cases appear during winter months. In general terms, what I feel may be happening, is that as Iodine demand increases and more is locked away inside macro algae tissues, the system starts to starve. Acropora's start to struggle as insufficient levels of free iodide start to hamper proper cellular function, which slows the transportation of nutrients. With this, there is a decrease in protective pigmentation, and the coral becomes more and more susceptible to UV damage from powerful lighting. Ultimately fading and tissue damage increases to the point where the coral may become susceptible to tissue infections or bacterial and algal bombardment as the coral suffers from a reduced ability to slime off unwanted coatings that would normally have been held in check by a protective mucus, or sloughed off. Manual Dosing using non branded bulk chemicals. Firstly let me stress how important 'testing' is. Not only in the case of normal additives / chemicals, but especially in the case of Iodine. If you get it wrong, don't test, or simply go overboard with Iodine, you will cause yourself more trouble than the exorcise was worth. especially in relation to the encouragement of problem algae spores that may come in on coral shipments or from other local hobbyists. at levels reaching 1.3ppm, you can cause limiting effects on filtration and smaller organisms, and excessive moulting and the premature death of crustaceans, so in effect, your filter will crash before your fish or corals.. In the event of you suffering the SPS symptoms listed above, and after all other tests have been completed to rule out other possibilities such as Po4 suppression or pH instability. I would suggest a possible course of action as follows. Personally, I can only attest to the Aqueous iodine method, I cannot attest to Lugals solution as I haven't tried it. aqueous iodine is available online through chemicals companies, in a solution as follows under the banner of 'Aqueous iodine' (iodine BP 5.0% w/v and potassium iodide 10.0% w/v held in a solution of distilled water) Add Aqueous
Iodine at a rate of
0.75ml each ‘day’ per 200gall
until you get a reading back near NSW, and then switch to 0.75ml per week
for a couple of months after that testing continuously. gradually trailing
to 0.75ml/200gall/month thereafter. (if Needed) (but keep testing as an
overdose can be just as dangerous as a depletion.) I'll hazard a guess
that for half the year, normal water changes will suffice quite
adequately, but during the summer months with increased Algae growth
supplementation may become the norm for many heavily stocked and
powerfully filtered set-ups. If using this method, please be aware of the need to test for 'total' iodine concentrations, and not just Iodide, or Iodate...It is quite feasible if using an Iodate only kit, to completely miss the fact that you are dosing and its being converted to Iodide by your DSB. You will keep dosing looking for a reading, whilst your iodide level is climbing to unacceptable levels so please be warned.
To surmise. I would strongly advise caution in all cases where Iodine supplementation is concerned. and if your seriously in doubt, then revert back to old school methods. i.e. up the quantity and frequency of water changes until your happy with what your seeing. It is very common for people to claim that corals look better and have more colouration when dosing iodine which is fine, But you cant always go on appearances alone, and a quick improvement shortly after adding iodine doesn't necessarily mean that your system is depleting it as fast as you are repeatedly adding it. It can turn round and bite you in the butt if you get complacent and just start chucking it in willey nilley. Ultimately.....Test.. I hope this page has been of some use to you. Simon.
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