Well my friend I think we will always disagree on this subject (and that is not a bad thing) another reason I like to have the heaters in the tank and not in the sump is that you can put two heaters such as you have in the water flow, such as the outlet from the filter, or in the stream of a power head at oppisite ends of the tank. Having water flowing directly past the heaters more quickly and evenly disperses heated water throughout the tank. In your sump the heated water has to pass through your return pump through your pipe work and out your effluent. And if you are using a protein skimmer some of the heated water heated water is being recalculated back into your sump and perhaps giving your heater a false reading