what i think you should do is get some peat moss and just mix half and half. thats the safest way cause i never tried to use just perlite. and as for watering i say you stick either your pinky finger or ever a toothpick about 2 inches down and if its completely dry then go head and water. Also when u water try not to just dump water in there grab like a ketchup bottle or something that squirts slowly so you have more control over what your doing.