Iwaki RLT type aquarium pumps handle back pressure better and can be used for almost any application. Especially recommended for high-head situations or when using cartridge (pressure) filters.
Iwaki RLXT type aquarium pumps are best suited for circulation only - that is, where water encounters very little back pressure--for example, returning water from a sump. Excellent where a high turn-over rate is desired.
Iwaki WMD aquarium pumps have American Made Motors