Glow squid spawning can conflict with hostile mob spawning when there is flowing water. Many hostile mob farms require that there is flowing water to move mobs, but it is impossible to separate glow squids because the light level needs to be 0 for hostile mob spawning. 

One solution to this would be to have Glow Squids have an additional water source block or body of water requirement like most aquatic animals in minecraft. Comparing this to the real world, it would make more sense to find squid in deep still water than shallow flowing water as they are unable to survive in rapid current.

Check the attached screenshot and world file