Humidity of 15%

My relative humidity is 15% Ive put tubs of water in the growarea but its still not rising.The room Temp is 80F Cant understand it why it is so dry. The plants are only small so I'm hoping it will increase as they get bigger. Is this dry humidity usuall or can it harm plants. Any info would be appreciated.
Have started spraying them with a very weak solution of seaweed. Should of mentioned I'm growing in a soil/pearlite mix I covered top layer of soil in pearlite to prevent evaporation.Maybee this was a mistake at this early stage of growth.

 

Thatd an interesting Q, buff I've often wondered about that. Here on the lost coast I feel lucky to see humidity under 50% usually it's 60-80%. A humidifier might work.

 

i had the same prob. i hung two towels above a tub of water. hang them so any water drips into the tub. keep the tub half full with water and simply lift the tub up to wet the towels then put the tub back under the towels and let the water run off at first i was wetting them 2 times a day but as time gos on you need them less now im venting like fuck to keep the humidity down. as you repot your plants into bigger containers they will hav more water in the soil to evaporate thus higher humidity also the plants kick out a lot of water them selfs when they get bigger. plants in veg do need around 70-80 for fast growth but your should drop it a bit later on. hope this helps mate it sure worked for me

 

Make sure your bucket are more like a pool, I mean make sure that they have a large surface of water exposed to air. If you have the room for it, you can use a kiddy pool or something to that effect. Than you train a fan directly to the surface of the water. The more the water ripples from the fan's air movement, the more evaporation you'll get. This will not only increase your grow's RH levels but it will also help keep your grow cooler. As water evaporates, it sucks a lot of heat from around it and turns it into kinetic energy. This kinetic energy is turned back into heat when the vapor condensates back to water so you have to make sure the RH doesn't so high that you can see condensation in your room but this is certainly not your problem.

Also, put in some salt in your water, this will help the water evaporate. As it does evaporate, the salt stays in the tub so you don't have to keep adding salt when topping off the tub.

 

The more plants you have the more humidity there will be, since plants transpire.

The greatest reason why the plants like to have a high humidity has more to do with the speed that the nutrient solution evaporates through the plants foliage and through the soil.

It's possible to grow fine specimens in low humidity but they will be really thirsty and you will have to flush often to reduce the salt buildup.

Many strains of sativa are native to places like Mexico and India which are hardly considered tropical places.

Aside from that, one of the first things I would do to increase humidity would be to seal the room better. Unpainted wood or drywall will absorb alot of moisture, which is precisely why it has to be primed before painted even.
1" thick styrofoam insulation is a good way to help. It's also a very effective reflective surface. You could use thinner styrofoam sheets if you can get them.