They will reproduce in your tank like crazy if you are not careful, even from only one individual. Another thing to note that I have experienced is that in cycling tanks I have a population explosion of pest snails and once I introduce the main aquarium inhabitants the population stabilizes provided you are not overfeeding. I think this is due to the fact that the snails have little to no competition with food sources while doing fishless cycling.
However, I have personally had bladder snails in my tanks for over a year (with no overpopulation issues) and I have found ways to control their populations if you cannot get rid of them all. I call them my four tips for successful pest snail keeping
1. Do not overfeed. Overfeeding
fish food or any organic matter will result in a population explosion in snails as they will utilize the extra nutrients to expand their colony.
2. Control their populations by picking up natural predators if your tank size and stock permits. Various
Loaches and Assassin snails make great inhabitants if your bladder snail population gets out of hand.
3. Manual removal by placing a blanched veggie in the tank at night and taking it out the next morning. Bladder snails are opportunistic and will eat most anything they can find. You will be able to remove good chunks of their population by doing this.
4. Regular fish tank maintenance. This is the biggest factor, regularly cleaning the tank and performing
water changes will remove some of the waste and detritus that builds up (a food source for Bladder snails).
Ultimately, I agree with Salem completely. Bladder snails IMO are not as bad as many point them out to be. They are great detritovores and algae eaters and with a little fine tuning on your end they can actually provide great benefits to your tank overall.