Hi mate,
That's excellent advice from 'mogthemackem'. Just another bit of advice for you to help keep them in good nick : Keep some sea water in your fridge as well, so that when you change the water it will be at the same temperature as the water you discard. I use a couple of 2 litre plastic milk containers, which I replenish when empty. Ragworm can be kept in the same way and are easier to keep than lugworm, but as the last post states; with care they can be kep for a few weeks. One last thing : don't put too many worms in each tray. The fewer in the tray, the easier to keep. Good luck mate.