Rod Venger, the originator of the idea before getting out of orchids, told me that he had to maintain heating mats under his containers, as if the water temperature dropped below 70°F, he had problems, and he had to maintain algae in them, or the smell was horrific.
Based upon my experience with s/h culture, I suspect that if he had changed the water often, that might not have been an issue.
Keep in mind that orchids do much of their gas exchange through the roots, so the chemistry of that solution will change rapidly, which is another reason for frequent changes.
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