Further to the post about sourdough starters being ready where there are photos and some marvellous commentary, here’s the very short movie that actually shows sourdough starter being spooned from the bowl and dribbled into the water.
Don’t coax it to float. Grab a spoonful of the refreshed sourdough starter and dribble it in the glass of water. If it floats – it’s done. If it does not float it is either not yet ready (be patient, wait a little longer), or is too far gone (give it a feed and start again, using any left over in some “normal” bread with added yeast to make it rise. It will taste lush).