Ok, while I admit that submersible pumps have their place, I don't like them and here's why. They add heat to the water. They are louder than externals. They don't last as long as externals. Although they all say they can be used externally, I don't trust the seal/gasket on any of them I've ever looked at. If you don't have room for an external pump, then a submersible is a valid option. Submersibles are cheaper than externals. They are fine utility pumps for doing water changes or as a backup pump. Externals are quiet, last a very long time, and add very little heat to the water. I've had good luck with Blueline and Little Giant pumps and, although I haven't used one, I know that Iwaki makes excellent pumps.
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