This is a difficult question to answer. I do have a rainwater tank to water my orchids but to make up for the lack of chemicals in that water I use an orchid fertilizer with a range of trace elements.

As for the Chlorine, who knows! but for years i used the water provided by Sydney Water and my large Cattleya collection grew and bloomed.

I think the Chlorine, pure water thing is a bit of a myth though there are some species that are fussy about water quality.

Not solving your problem but i suspect Chlorine is not the cause though if you think it is you could store your water from the tap for a day or two to let all the Chlorine evaporate before use.

Your RO system has a prefilter that removes Chlorine and Chloramine. If that fails these 2 chemicals destroy the membrane of the RO unit. If you are getting RO water, the chlorine has been removed.

Have you tested for virus and what are the roots like?

Nick

Has anything else changed? Have you gotten a new heating system, or perhaps the old system isn't working quite as well as before? Have you switched to a different fuel? What other changes have taken place that might affect the orchids' climate? A friend was suffering a decline in her orchids for a couple of years until she discovered her propane tank was leaking.