I think incorrect soil is my most likely bet. I give them same soil as my trichocereuses and they like lots of organic matter.

Thanks, i will immediately start looking for better soil and repot them asap.

I don't think its mite. But is there any way for me to check that ? There definately no tiny insects walking around on them.

edit:

i found this link. Recipe for cactus soil mix

that should help.