This movie defies all logic.
You would not be able to see a diamond ring at the bottom of the pool with water in it.
If a diabetic has low blood sugar, they don’t take insulin, they eat. Insulin lowers blood sugar, it’s used after a meal sometimes.
The janitor would not have to sign into the phone with the passcode to call for help. There is emergency SOS’s on every phone, it’s been that way for a while. Also I’m sure the indoor pool would have a phone on the wall somewhere.
If nothing works, you could easily use a voice assistant like Siri, or Google, to call for emergency services, assuming this movie takes place in a modern time.
Lastly, most indoor pools do not need covers, this defeats the whole purpose of the indoor pool.
Do not waste your time watching this movie. It’s too tense, and irrelevant.
(No hate to the actors, directors, and film-producers.)