Originally Posted by LauLanChu

Though it may be due to upkeeping, SBD is sometimes intrinsic genetic problem...no matter how you do, it will still get SBD when it ages. Did you notice some fishes are more hardy and some are very prone

Due to X-breeding, globoid body are created (e.g. ranchu, lionhead) and these breeds are very prone to SBD. On the other hand, those of conventional type (e.g. comet, wakin..) with longish body have more resistance against this problem.

Therefore, problem is there and how to select a GF without this hidden problem is very important. So observe how the fish swims for any slight sign of SBD before you buy . You may even try to stir the water to observe how the fish swim against the current. I am not able to tell you exactly how to see, but a very simple principle is whether the fish can swim straight.
This is very important thing to do to avoid future headache.