when you go to the hardware store buy a hydrometer. Get the syrup to the correct brix. Also get a felt cone filter and a few pre filters. They sell all of that stuff. Sounds like you are getting more sand when cooking on the stove. Filter it once you get to the correct brix and then reheat and keep the temp of the syrup under 200 when bottling. it helps to also have a thermometer that reads in tenths.