Clay Pots are like sponges, the clay, during it's time in the ground, absorbs all sorts of minerals, when it is fired and turned into a pot, all the moisture is pulled out of it, so when you put a nice wet bog in there, the water gets in, and pulls more minerals into the pot. eventually, the pot will start returning those minerals to the media in an effort to balance out.
Also, clay pots tend to get rather nasty in their appearance after a while of being wet, the salts in them will start to crystalize on the outside of the pot, making a white nasty stain.
You CAN use these pots however. I'll tell ya what I did was simple. I bought a huge cylindrical clay pot to use for my mini-bog. Then, I went and bought the waterproofing paint that you use on garage floors, it repels EVERYTHING, (even oil and what not) I think it's made by Bher, I can't remember, anyhow, I put two quick cotes of this on the INSIDE of the pot and this formed a water tight barrier that the bogs fluids could not penetrate.
I know this stuff works, and is safe, because before using this pot as a bog, I used it as a mini-pond with goldfish in it. that lasted for two years!
So simply waterproof the inside of your pot. (Note, do not use thompsons or other oil based/wax based sealers, they won't last. Use the paint.
