As it relates to bromine. Finding Bromide in ICP or lack of wouldn’t suggest that particular OPO might be present or guaranteed it’s absent?
No.
Ozone converts bromide into more oxidized forms, but the total bromine element concentration is unchanged:
Halogens
When ozone is applied in seawater in concentrations higher than are naturally present, a larger variety of chemical reactions take place. Chief among these is oxidation of bromide to hypobromite:6,7
O3 + Br- --> BrO- + O2
BrO- + H2O --> BrOH + OH-
The first reaction is very fast, and the half life of unreacted ozone in water with a lot of bromide (such as seawater) is on the order of a few seconds.8 Because hypobromous acid's pKa (in freshwater) is about 9, it is primarily in the protonated (uncharged form) in seawater, but a significant amount of BrO- is also present.3 The hypobromous acid is itself a strong oxidizer and can rapidly oxidize other organic or inorganic materials.4
The hypobromous acid can also react in a variety of ways (including disproportionation and additional oxidation with ozone) to form bromate:
BrOH --> --> --> BrO3-
The hypobromous acid can also be catalytically broken down by ozone to return to bromide:
BrOH + O3 --> 2O2 + Br- + H+
About extensive ozonation of seawater, one group concluded:
"Ozonization of seawater oxidizes bromide ion to Br (hypobromous acid and hypobromite ion) and then to bromate. If seawater is ozonized for >60 min, essentially all bromide is converted to bromate."9
That level of ozonation, however, is far more than would take place in a reef aquarium. The various reactions leading to bromine-containing byproducts of water's ozonation have been extensively studied (especially in the context of disinfecting fresh drinking water that contains bromide). Nevertheless, it is a complex problem. One recent review3 stated:
"Because bromate formation during ozonation of bromide-containing waters is a highly non-linear process, kinetic modeling has been applied to improve mechanistic understanding and to predict bromate formation. The full model consists of more than 50 coupled kinetic equations which can be solved simultaneously with a computer code…"
and then went on to say,
"the predictive capabilities of such models for the ozonation of any water should not be overestimated."
Well, we won't try to calculate what happens in reef aquaria, but we will conclude that bromate and hypobromite may be significant.
Bromate is typically the longest lived after ozonation of bromide-containing water. It is, in fact, one of the biggest concerns with ozonation as a purification method for drinking water, because bromate is a suspected carcinogen. For this reason, the US EPA limits it to only 10 ppb in drinking water. So in considering the properties of the treated seawater in aquaria, both BrOH/BrO- and BrO3- must be considered.
There is at least one study in the literature of bromate in a seawater aquarium.10 Here the ozone was used for disinfection, so the doses used may be higher than many aquarists employ. I also do not know whether or how effectively they treated the post ozone water with activated carbon. Nevertheless, the bromate levels in the Living Seas exhibit at Walt Disney World's Epcot Center were tracked. The researchers studying this display found that bromate had risen to about 0.6 ppm (with nitrate at about 600 ppm). After adding a batch denitrifying system, the bromate and nitrate concentrations began to drop, suggesting a sink for bromate that might well exist in many reef aquaria as well (that is, in systems or locations where denitrification takes place).
The same reactive pathways that lead hypobromous acid to bromate will take hypoiodous acid to iodate.
IOH --> --> --> IO3-
In the ocean, iodine's predominate form is iodate (IO3-) with a smaller but significant fraction of iodide (I-). These two forms' bioavailability to macroalgae and other organisms varies from species to species, but iodide is often more bioavailable than iodate. Regardless, the use of ozone will likely skew the fraction of total iodine toward iodate and away from iodide. That may or may not be important for reef aquarists, because the importance of iodine's availability from the water column to organisms kept in reef aquaria is undemonstrated, but it may have strong implications if test kits are used detect some species and not others.
This concern was studied by one group in the Smithsonian National Zoological Park's Department of Animal Health.11 It claimed that fish need iodide in the water column in the form of iodide to make the hormone thyroxine. Regardless of whether that is true or not (that is, whether fish need iodine in the water or whether they can get it from food), they showed that seawater's ozonation to an ORP of 400 mV (equivalent, they claim, to the level attained by skimmer driven use of ozone) reduced the iodide concentration by more than half. Ozonation also decreased the concentration of organoiodine compounds, and raised iodate levels. In the aquarium itself, iodide and organoiodine compounds were not detectable when using ozone. They go on to suggest that iodide supplements might be beneficial in cases when ozone is used. Therefore the conclusion that "iodine is an unnecessary additive for reef aquaria," when that conclusion is based on success in aquaria not using ozone, may not extend to aquaria that heavily employ ozone.
As long as bromide remains in the seawater, the equivalent reaction of ozone with chloride
O3 + Cl- --> ClO- + O2
is unlikely to be significant as it is much slower than reaction with bromide. The small amount of ClO- that may form can react with bromide to form BrO-.3,6,8
