In my survival world I've carved out an area for a chunk-based slime farm. I know that it is a slime chunk, so please do not comment about that. I don't know what I did, but the farm hasn't produced a single slime. Does anyone have any ideas as to why this is happening? Screenshot is attached.
You need to be at least 24 blocks away from the spawning pad for them to spawn. Also, light up aboveground within 128 blocks. Your farm looks small. Slime farms take lots of hard work. Try expanding it by making more pads, as lotus49 pointed out.
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Biome (other than swamp, and that's only when you're on the surface) has no effect on slime spawns.
1)check your render distance. Anything below 10 reduces mob spawns, and at around 6 you may as well be playing on peaceful (mobs will be very, very rare).
2)light up more caves. 1.8 (possibly some of the 1.7 versions, too) has a LOT of caves that don't connect to anything, or which connect to other caves in a weird or unexpected fashion. Without gridding your way through the area or using some sort of xray feature (mode, glitch, or the official spectator mode), it's practically guaranteed you did not at all manage to light up anywhere near most of them, much less anythihg approaching all.
Another thing to check out along with lighting is the existence of nearby slime chunks. You have to check for them in the same radius as your cave-lighting, but since slimes spawn in any light level you will have to either fill in the space, place bottom slabs or similar unspawnable blocks, flood the area, or dig out the entire chunk down to bedrock.
3)make sure you did not accidentally build your spawning platforms using bottom slabs. Mobs cannot spawn on glass, leaves, tile entities (anything you right click to get an inventory or do something special with), in liquid, or on any partial block that has airspace in the upper half of the block (stairs, fences, gates, etc). They can spawn just fine if there's a torch there, but pack spawns can be blocked by such things.
Update: I have spent so much time lighting up caves surrounding the area (screenshot attached) but I am still getting little to no spawns. I added another layer, like recommended, for a total of 3. I also have made sure that the area I wait for spawns is more than the required amt. of blocks away. However I am still getting little to no spawns, and I am getting very frustrated. Thanks for all of your help, and any further suggestions are welcome.
*I have also flooded nearby slime chunks and blocks in the chunk I am using that are not spawn pads.*