Update time
Been a while since I had a few minutes to update. Will try to answer a few questions and go over some problems i've had along the way.
First and foremost, DO NOT use tap water with a fogger in a closed system!! Learned this one the hard way after I noticed my big can fan wasn't pulling a lot of air like it used to and I was getting white particulate matter on the plants. Opened up the Ice Box radiator and it was COMPLETELY caked with minerals!! I wish I took a picture but it was an absolute mess, couldn't believe any air at all was passing over it. So I cleaned everything out and switched to RO water for the fogger and it works fine. So yes you can use RO water. No mineral build up and no white stuff on the plants making you think you have aphids/mealy bugs.
Have installed a RO system at my water supply around the corner so no more buying water and now have all I need to refill the humidity/fogger tank. It goes through about 12 gallons a week or so keeping the daytime humidity at 70-75% and is off all night and the box stays around 70% on its own.
I've had one episode of rot on Paph Mount Toro (philippinense x stonei) that occurred after I tried dropping the temp in the box down to 55F to give them a cold shock around christmas. Was able to save it with aggressive cutting of rotting leaves and physan, didn't spread to any other plants. Leaves started going red which left me baffled for a little while until I realized to was getting cold in the box (automated system I sometimes forget what its set to and had set it up a long while before that to do the cold shock). Shortly after the colour change I started seeing the rot. Thanks to John M for some help on that one.
System is now up and running on 600w from the extended spectrum MH with no problems and great growth so no I don't think the light is too strong or overkill with proper humidity and great air flow. Plants aren't showing signs of stress from the light, have the strap leaf paphs taking the brightest spots and the little guys grabbing some shade under the bigger leaves and off to the sides. Edit: as the light has been going strong for over a year now its efficiency has probably dropped considerably and the now 600w might be more like 400w from a brand new bulb, will have to look into replacing it soon I think.
Energy efficiency: I cannot provide any numbers but feel the water cooled system is a nice way to avoid the terrible drying effect of air conditioners. I have read some random internet posts that water cooling is quite efficient. The water chiller does not work very hard keeping the water down at 55F but it does have to have a pump running water through it 24/7.
Automatic watering: abandoned completely. If I go away I have orchid sitters come and water and I monitor the system remotely through the Ecozone that now has its own IP addy for remote access. If anyone wants to have a look at the online system fire me a PM.
Couple other casualties along the way: Paph. Chiu Hua Dancer (sanderianum 'Henry’ x gigantifolium 'Dark Warrior’), Paph Armeni White (armeniacum x delenatii) and a Paph delenatii. All just generally failed to thrive, didn't have a good explanation for why, roots seemed pretty good. Was really sad to loose the Chiu Hua Dancer.
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