Ring around the jet

[Jsf721]

I’m looking for a leak and was re checking the screws on the skimmer box and jets. One split. Can I replace this under water or is this something I need to drop water level to replace.

So you think this causes a leak ?

 

[Texas Splash]

You'll need to lower the water level to repair that jet so that water doesn't pour out. My return line tilted after a few years and one fitting cracked inside at the threads in the 12 O'clock position.