Black spots on several orchids

[Cymbidium]

Hello,

within the last few days tiny black spots have grown on the leaves of quite a few of my orchids.

I've already read a few articles about pests and diseases but it's still really difficult for me to say what this is and how to treat?

The plants are in different rooms. Every cachepot stands in a pot saucers with some water to provide a higher humidity as this had been recommended to me by one orchid seller. Currently I am afraid that this might be the reason for a fungal infection.
But once again I am unsure if it is a fungal or bacterial infection and how to treat it?

Any recommendations?

[Ray]

Acidovorax, maybe?

[Roberta]

I do suggest not letting them sit in water. Much better to water well (running out of the bottom of the pot) then drain well. That will pull air into the root zone and flush out accumulated salts and other junk that you don't want.

[Cymbidium]

It didn't got any worse over the past few weeks, so I guess nothing to worry about.

Roberta, as I am using osmoses water it's quite difficult to produce the amount of water I would need to water all orchids the way you propose. But anyway, I've started flushing them with tap water every now end then.

[Roberta]

Unless you tap water is REALLY bad, Cymbidiums don't need RO water. Which is good because they are big and thirsty. In the area where I live, people grow Cyms with tap water that is 500-600 parts per million solids (calcium carbonate being the largest contributor to that total) My water is better but not wonderful. If you are near the ocean and have a lot of sodium in your water those levels of solids would be bad, but high calcium is no problem. There can be some browning of leaf tips if solids are high, but otherwise no harm to the plant.

[Cymbidium]

My tap water has 350 µSiemens which should be about 220 ppm TDS. Other than that I do not have any more information with regards to the elements in my tap water.

[Roberta]

Your water is quite good enough for the Cymbidiums (and for many other orchids as well) I would suggest saving your RO water for those types that really do appreciate it.. Pleurothallids especially. Also Miltoniopsis and some of the other Oncidium tribe like pure water. But Cyms really don't care - your water is quite good (no matter what the exact mix of minerals, nothing is very high)