Strange artifacts from blending textures

So I've tried to add another texture into my texture mixing machine(*cough* The shader). However, being a noob in this area, I can't understand the logic error in my code. I seem to be getting very bad alpha artifacts? My script works, with two textures. I simply can't transfer that logic into three.

*SEE NEXT POST FOR UPDATE*

Here is a screen shot and the code:


Strange artifacts from blending textures