Humidity

I have my house plants in my fish room. The room isn't exactly huge, but my fish tank is! It is a 360 gallon monster, and with the filtration system the total amount of water is around the 400 gallon mark. There are three heaters in my tank to keep the water around 25°C. So, that given, you'd expect the humidity in my fish room to be jungle like?

The air temperature in my fish room hovers around the 22°C mark, and the humidity at that temp is around 40-50%, according to my little monitor, how accurate it is I don't know.

I also have a small electric heater on a timer and have been doing a couple of experiments, with surprising results, to me anyway.

When I raise the room temperature the humidity goes down, no lower than 40% though. When I lower the room temperature the humidity soars, sometimes as high as 70%!! This seems crazy to me.

I thought higher humidity comes with heat, especially when you take into consideration I have a 400 gallon source of warm water in the room!!

What room temperature/humidity levels are considered best for house plants?

 

I've always understood it to be relative humidity, so relative to the temperature.
Warm air can hold more moisture than cold so the RH alters with the temperature.
I don't profess to know how to explain it correctly, but dew point comes into it as well, when the temperature drops to a point where the air cannot hold the water it is carrying and it forms fog.

So the humidity stated will always be at that temperature.
Plants of different types like different humidity levels, cacti and ferns are the best examples of the extremes but even they have variations amongst them.

 

@Esoxlucius The humidity is the % of the maximum amount of water (mbar) in the atmosphere. For a given temperature there is a certain vapour pressure of water (31.7 mbar at 25°C) at this temperature 100% humidity = 31.7 mbar of water and 50% humidity = 15.85 mbar.
The vapour pressure of water is strongly temperature dependent reaching 1013 mbar at 100°C. As the water temperature in your tanks remains constant at 25°C the maximum vapour pressure of water is 31.7 mbar. The maximum amount the air can hold away from the tanks depends on the room temperature so as the room temperature goes down the humidity goes up.
Too increase the humidity you could increase the water temperature or increase the air circulation over the surface of the water and the rest of the room.
Neither of these are things you might want to do.
As for the house plants their preferred humidity depends on where they come from, so cacti and other plants from arid regions drier and from jungle areas prefer higher humidities.
The easiest way to increase humidity around plants is to stand them on a layer of gravel with water in the bottom of the container and the base of the pot above the water.
The most accurate way to measure humidity at home is to use a wet and dry bulb thermometer.

 

If you had 100% humidity, that means the air is unable to hold any more water, so the water in the air would be forced to condense back into water droplets.

Higher air temp has higher water holding capacity, hence the percentage drops as temp increases.

As a hopefully interesting aside, this phenomenon is why you hear stories of the jungle being awful while a sunny beach at the same ambient temperature is nice. In the jungle, you will sweat as your body tries to cool itself, but the sweat can't evaporate because the air is already holding as much water as it can.

 

Think we would be more concerned about condesation in the room and how the room air temperature affects that, rather than the plants as would think many plants would enjoy that kind of humidity/temperature, perfect for orchids etc.

When used in a garage extension we enclosed the top of the tank and extracted all the moist air to a vent as in winter the condensation was too much.

Is it an external fish house or in within the house ? wondering how much direct sunlight the plants will get ?

Assume its a marine tank and guessing its something like 6 -8 ft long ? we like pics !

 

Not marine, freshwater. The room is a north facing garage conversion, plenty of light but no direct sunlight at all. All my plants are on the window sill except for a kentia palm (floor), and a mother in law's tongue (mid room on a small cabinet).

The tank itself is a fibreglass tank with a single viewing panel in the front. It's roughly 6x4x3.

 

Wicked ! can see you have one of our favourite fish the Clown Loaches in there and able to grow to their full size. The larger ones being Oscars ? though not sure what the biggiest one on the right is ?
You must have a massive filtration system in there to cope with such a high fish to volume ratio.

Plants like Orchids, African Violes and Cape Primroses should enjoy a humid north light, though you could always use some of the cheap led plant grow lights to increase the range.

 

Yes, there are 11 clown loach in there. They are one of the longest lived fish in the hobby living up to 25-30 years. I've had mine 8 years or so, so they are still babies yet!

No oscars though, they are too predatory and would eat a lot of my smaller fish. The two you are probably referring too are cichlids though, both very peaceful, a chocolate cichlid and a red shoulder severum.

The really big one is a red tailed giant gourami. He's about 20" long, I've had him about 8 years too. We bought him when he was about 2" long.

The filtration system is a huge four tier crate trickle filter housed within a 50 gallon HDPE barrel. Top crate has filter floss and various grade sponges for mechanical filtration. The middle two crates are full of various types of bio media for biological filtration, and the bottom crate houses my return pump.

I wish I was as clued up and experienced with plants as I am with fish, lol.

My current plants are calatheas, bromeliads, a mango sapling, a pomegranate sapling, a spider plant, a young livistona rotundifolia palm, a Calla lily, a mother in law's tongue and a kentia palm. I also have a parlour palm in another room.

All my plants are doing well, especially these past two or three weeks. You can tell spring is here, they've quickly started pushing growth out.

I just couldn't get my head around the whole humidity thing, but there have been some good replies in this thread which have helped me understand it a little better.