Above ground pool

We have a 50000L Bestway pool which has been up for 4 years. It is great but there is a bubble starting to form on the floor and dont know if thats the start of liner problems or not. But, it only cost $1200 and is big enough to do small laps in, we have definitely got our use out of it so if it only lasts 5 years it's been worth it. More chlorine than built in pools because the water temperature is a bit warmer which is also the reason for evaporation so keep a cover on it when not using it. Our local pool laws allow no fence if the above ground pool has walls that are 1.2metres high and the ladder is kept either fully in the pool when not being used or locked up, ours is 1.3m but we still have a fence.