Ultimately, what is more important; humidity or airflow??

[ColoradoBirddog]

So I've got a number of my tropical orchids in a 75gal tank. I'm running a 400w HPS over it. For humidity, I've got 3 inches of hydrotone pellets and water, as well as a reptile fogger. Temp is routinely 80-85°.

Currently, I'm running 2 smallish fans. One inside the terrarium, the other on top drawing in fresh air. The rest of the terrarium is enclosed with glass.

If I stop running the top fan, I'm able to get the humidity very high, at least in the 70-80% range. If I run both, I can keep the humidity in the 50-60% range, sometimes higher. But, often it drops as low as 30%. It takes a little bit of watering to keep over 40%.

So, ultimately, which is better for the orchids? Higher humidity and less airflow (but still some), or higher airflow with a little lower humidity?

[camille1585]

The answer will depend on which orchids you have in the terrarium, and generally both air circulation and decent humidity are needed. Also, your question is more about whether fresh air is needed, since you have another fan recirculating the air within the terrarium.

How long/often is the top fan running? I don't have a terrarium so can't advise on the specifics, but it sounds like your top fan is either overpowered, running too long, or badly placed. Running the top fan a couple minutes at a time several times per day can be enough to bring in fresh air but prevent the humidity from dropping too far.

Keep in mind that when we say that airflow is needed, it's not a strong wind nor visibly moving leaves! You just need to keep the air lightly moving so that it won't stagnate. Your recirculating fan probably manages that.

[ColoradoBirddog]

The orchids I'm growing in it are Catts, LCs, Phals and a Neofinetia.

So, if you can picture, I have a small "room" fan inside, at the bottom of the tank, running 24/7. Coming in from the top is my fogger, and then a glass panel that is set open, the entire width of the tank, for about 4". Finally, I've got a brushless computer fan bringing in the fresh air, again for 24/7.

In that manner, the airflow is very good, but like I said, getting a little drier than what I think would be good.

Since starting this thread, I'm experimenting with just using the top fan, 24/7. But, any input is appreciated.

[Ray]

What kind of fogger do you use, and how is the fog moved into the tank?

Seems to me that if there is any kind of fan moving the moisture into the tank, it must be moving some air, too, making the fresh air fan redundant.

[ColoradoBirddog]

Ray, it's a small reptile fogger, and its delivered via a plastic tube. I dont believe it would be enough airflow.

[Ray]

Oh well....

[ColoradoBirddog]

Did I miss something Ray?

[Ray]

Originally Posted by ColoradoBirddog

Did I miss something Ray?

Yeah... "Oh well"... I guess my thought that maybe you don't need an additional fan does not apply.

Another thought: Do you have to completely enclose the top? If there is a small/moderate opening, the tumbling air from your fan might result in enough exchange, while the humidifier can still do its thing.

[ColoradoBirddog]

Yeah, the way I've got it set up, there is about a 4x10" opening, with the intake fan in place. If I remove it, I can pretty much have it as open or closed as I like.

[Ray]

Originally Posted by ColoradoBirddog

Did I miss something Ray?

Yes. What I meant was that it's too bad more air isn't brought in with the fog.

Another thing to consider: Must you keep the entire top closed? As you have a fan operating, the turbulence it creates will create air exchange through any opening in the top, and it may be that your fogger maintains a decent humidity anyway.