In a deep enough pool (8', 12', etc) yes, you can get an ear barotrauma. But you're gonna get PAIN first! If it hurts, STOP, go back up, and clear!
You can EMBOLIZE in 3' of water. DON'T hold your breath!
The other issue is infections. Here it is a question of maintenance. If the pool is properly maintained and the water balanced, it is no problem. If its not, you can get a NASTY infection. Pseudonomas, one of the worst bacteria around when it comes to making you nice and sick, will grow quite well in a pool if the chlorine level is insufficient. Excessively high chlorine levels or out-of-whack pH will make your eyes hurt, but probably won't actually do HARM (other than being uncomfortable and possibly bleaching hair, your suit, or your dive gear!)
A pool used for commercial purposes (a dive shop qualifies) should be tested DAILY at a minimum and pH and both free and total chlorine level logged. The water should be crystal clear; if you cannot make out the face on a quarter at the bottom of the deep end, its not clean enough on a particulate basis.
Free chlorine should be at least 1.0ppm and not more than 5.0ppm. Total chlorine (chloramines + free chlorine) should not be more than 1-2 points above that, or you will have problems with your eyes burning and possible skin irritation (free chlorine does NOT cause burning eyes - chloramines do. Chloramines are the compounds that chlorine forms when it "burns up" organic matter, including bacteria and virii.) High chloramine levels are not dangerous, but they are annoying and a sign of poor maintenance or too many swimmers for the pool's water filtration, total gallonage and chlorine content.
pH should be between 7.0 and 8.0. Levels under 7.0 are very irritating, above 8.0 and chlorine doesn't work well in sanitizing, which can be dangerous. Towards the higher end of the range (e.g. 7.8) is less irritating to the eyes than lower (e.g. 7.0 or 7.2)
An OUTDOOR pool (exposed to sunlight) should have a cyanuric acid level of 30-60ppm. Levels over 100ppm inhibit chlorine sanitization, and extremely high levels (which can occur if tablet chlorination is used) can actually cause some health effects directly. LOW levels will cause chlorine to "disappear" almost instantly in sunlight due to UV breakdown, making the pool unsafe in as little as 2 hours of full sunlight after chlorine is added in the morning or overnight. INDOOR pools (no sunlight) should not have ANY cyanuric acid content in the water.
There are other issues with pool water balance, but they have to do with the health of the pool hardware (shell materials, such as gunnite), pumps and plumbing, etc, and not biological safety.
DON'T swim in a pool that you have reason to believe is microbiologically unsafe.
Now you know more than most private pool owners and about half of commercial operators