I'm sorry if I just came online...I've been very busy with work. I went in here because I'm starting to worry about my paint brushes. After using one brush once, it gets hard even though I'm soaking it in oil/water/thinner and others. Please help.
What medium are you using? From the sounds of it, I would guess that you are using acrylics. Never leave acrylics sitting on your brush, because it dries quickly and because acrylic paint it isn't water-soluble once it dries. There are probably some nasty chemicals that can be used to get dried acrylics off of a paint-brush, but the brush will likely never be the same again.
It takes a lot longer for oils to dry, and turpentine can probably be used to loosen up dried oil paint in a brush, but again I doubt the brush will be the same after such a treatment.
Ultimately, you just need to be careful to never let your paint dry in your brushes, no matter what medium you use.
I think you are awesome, and I wish you the best in your endeavors, but I am tired of repeating myself, I am very busy with my new baby, and I am no longer a regular participant here, so please do not contact me to ask for advice on your career or education. All of the advice that I have to offer can already be found in the following links. Thank you.
Assuming you are using oil paints:
Dip your brush in some oil, and wipe off any excess paint. (water if you are using acrylic)
I repeat, DIP, do not STAB your brush in turpentine or oil... there is no need.
It just splays the hairs and lets paint get further in there.
Once you've wiped off the excess, just wash it gently under warm water with good ol' Ivory soap.
Keep lathering and squeezing out the paint until the lather remains clean.
Do this after EVERY use.
I have brushes that have lasted me for a decade now.