Mineral buildup
 

Yes, the buildup of minerals inside the warm mist humidifier when using tap water is something that has to be dealt with. Even with cool mist humidifiers the minerals in tap water are a problem but they just end up as a white dust all over the room instead of a crust inside the machine.

I deal with this by using Reverse Osmosis purified water. I used to buy it at a supermarket vending machine, several 5 gallon jugs per week. Now I have installed my own RO system at home.

I have only managed 55% or so in my home growing environments, but I find drying laundry helps!

With the windows closed on a cool day, it's pretty easy to raise humidity with a cool mist humidifier, like this one and/or mist fan. If you've got a big room (or greenhouse/conservatory), you can get big foggers that are really effective.

Just remember that with more humidity, you should have more air movement (fans) or you'll have trouble with bacterial/fungal rot.

If it's not ridiculously hot and dry outside, I can manage to keep the humidity level pretty much anywhere I want it, as the EvaMist unit has a hygrostat (like a thermostat for humidity).

I can even monitor it from work as I installed a network data centre monitoring device in the growing room, and if necessary, go home and do something if it drops to low. The system can even be set to email you if things go out of range (or you can use something like Nagios to monitor it and alert you).

Re: HUMIDITY: How to raise the levels ???????
 

I grow my Orchids all on one (1) large Windowsill - with a SOUTHEAST exposure. On the windowsill itself are all potted Neofinetia falcata and hybrids. On the side walls of the windowsill are Mounted Aerangis and Angraecum.

On the windowsill is a Cool-mist Humidifier, and on top of the humidifier is a Small fan which is on 24/7.

Above the windowsill is a Clamp-on Grow Light with a 2700k 40-watt bulb.

Given the types of plants you grow, a relative humidity of 50% should be adequate.

I've learned that keeping the humidity much higher can lead to mold growing on walls and wet spots on wood floors in areas that are shielded from the heat in the room.

I use a cool mist humidifier in a small room where I grow gesneriads and the plants do fine. The orchids in the greenhouse have a fogger that is set to go on if the humidity drops below 50%.

If you want to give the plants a little extra humidity, try misting them with distilled or RO water several times a day.