I use a 0.7kg weight and find it suitable for even the strongest curent. Always use a tangle free line from your decoys with a deep sea fishing line clip that can clamp on to the mother line at the other end. plenty of videos on you tube to help and some good British companies to get all your bits from, just make sure you shop about as a vast difference in price. I always put motherline out at low tide and put decoys on as I go.
Hope this helps