i use Forte lunar light tubes and they are great! i have had no problems like you are having and they are light (50g) so i couldnt be happier. my guess is it has to do with the installation. do as the above post stated and also make sure you do not tighten the nutt on the valve to much. you might also want to check your rim where the valve hole is drilled and make sure it doesnt have any sharp edges. if so sand them down.