This is a normal early-stage "false rise" caused by gas from bacteria. Keep feeding dailyactivity will return as yeasts establish. For a full explanation, read our article: Why Did My Starter Rise on Day 3 Then Stop?
Early on, this is common. Keep it warm (around 756F), feed consistently, and give it time. Use non-chlorinated water if your tap is heavily chlorinated.
A gray or brownish liquid that forms on top when the starter is hungry. It9s harmlessstir it in or pour it off, then feed.
During activation: once every 24 hours. After it9s active: daily at room temp, or about weekly if stored in the refrigerator.
Yes, if it9s not strongly chlorinated. If chlorine is high, use filtered or let water sit out uncovered for a few hours before using.
Active bakers: keep at room temp and feed daily. Occasional bakers: store in the fridge and feed weekly. For long breaks, dry a portion for backup.