I realize that there are supposed to be certain positives to using Chlorine Dioxide. And I'm pretty sure that there are some formulations that have taken care of or reduced the chlorate concern.
Among some of the positive effects of using chlorine dioxide that are of a particular benefit are those involving crypto and biofilms, and that it is treating the whole body of water. Chlorine dioxide is very effective against both at relatively low levels... something that chlorine alone does not seem to handle very well. However, there is a trade-off to consider before using chlorine dioxide. A potential problem that I have with its use that is rarely discussed, is in how it actually does this. It's able to permeate the outer shell of crypto, and the biofilm matrix because it is lipid soluble... meaning it is fat soluble. This of course is good for getting into the biofilm matrix and through the crypto outer shell, but maybe not so good for us humans, as it can also permeate the skin. Just a thought for our kids swimming health, as this is an area that still has many unanswered questions. More research is needed.
I agree with you Al that chlorine dioxide is useful against Crypto and biofilms and that it needs further study in terms of how it reacts with human skin, how deeply it penetrates, etc. More research is definitely needed.
This scientific paper determined the rate constants for chlorine dioxide reacting with a variety of inorganic and organic substances. For practical purposes, chlorine dioxide does not react with bromide ion so will not produce bromine from it (unlike chlorine that does). Chlorine dioxide does not react with ammonia (unlike chlorine that does). Chlorine dioxide will react with iodide to form iodine (so will show up as CC in that type of test; not sure if it shows up in the FC test at low concentrations). It will oxidize nitrite to nitrate (as chlorine does). It will oxidize ferrous ions to ferric ions (as chlorine does). It will react with ozone probably getting oxidized to chlorate.
Chlorine dioxide will oxidize many phenols which are phenyl groups (benzene rings) with a hydroxyl group. This means it will generally react with humic acids as they typically contain phenolic groups. However, chlorine dioxide will not react with urea nor with fumaric acid. It is slow to react with amino acids such as glycine, alpha-L-alanine, L-cysteine.
Because urea is by far the largest component of sweat and urine, followed by ammonia, the fact that chlorine dioxide does not react with (oxidize) such substances means that chlorine will react with these instead if both are present. Therefore, having chlorine dioxide in the water in addition with chlorine does not provide supplemental oxidation for the main chemicals in sweat and urine. It does provide oxidation for phenols and that may be useful for breaking down some kinds of lotions/oils that may contain them.
Chlorine dioxide is somewhat volatile so if used indoors with water that is agitated, some of it will come outgas more rapidly. Limiting chlorine dioxide levels below 1 ppm helps to keep the air concentration at safe levels.
Normally, when chlorine dioxide is proposed, it is to be used as a disinfectant in place of chlorine since it does not produce as many disinfection by-products. However, as noted above, it is not a strong oxidizer and is rather selective so supplemental oxidation of bather waste or its coagulation/filtration and physical removal are still required.