It seems to me that water that is not balanced make a person more prone to swimmers ear. Leaving water in your ears definitely contributes to swimmers ear

I got a tip from this site and use it every time I go swimming.

I have rubbing alcohol in a squeeze bottle and when we are done swimming we squirt a little in each ear. The rubbing alcohol mixes with the water left in your ear and evaporates. I have had no cases of swimmers ear since using this method.

Also knowing your CYA is really important. I would get my water tested at a new place if they did not test CYA. Or buy a good kit and test it yourself.