Minecraft – CraftBukkit and slime spawn chunks

Slimes can spawn in any light level, so having your area well-lit will not stop them.

However, just as with other mobs, slimes require an opaque block to spawn on top of. You can stop them from spawning by lining the floor of your area with transparent blocks, such as glass or slabs.

Additionally, the three sizes of slimes require different amounts of room (i.e. non-opaque blocks like air, signs, torches, etc.) for them to spawn:

• Big Slimes: 3x3x3 block area.
• Small Slime: 3x3x2 block area.
• Tiny Slime: 1x1x2 block area (or 1x1x1 if the upper block is not opaque).

So, another solution is to simply fill in the area as much as possible.

Slimes can only spawn in chunks where they are allowed. Why are there slimes in chunks that shouldn't have them?

1. Slimes move around. Chances are this is what happens. They will bounce (ooze? slide?) to different chunks over time. This can include falling from higher heights.

2. You used or read the slime chunk calculator wrong. Maybe you punched in the seed wrong or chose the wrong map. Maybe you misread your map? Double check you if you needed to have a "-" (negative sign) on your coordinates. Double check your calculator.

This may or may not apply to your spawning pads but slimes can spawn at any light level, unlike other mobs like skeletons, zombies, etc.

For reference: Minecraft Wiki - Slime http://www.minecraftwiki.net/wiki/Slime