Originally Posted by I<3Fish
I dont understand what a heater does without glass over it? Does it electricute the fish?
Possibly. Saltwater is extremely conductive. You should see what happened when I spilled some on a power strip. Lesson: Always have a SW tank running off a GFCI.
It's less likely to electrocute your fish if you don't have a grounding probe or anything else grounded in the water, and if the heater is in a sump or something other than the display tank. Electricity travels from the hot to neutral or the hot to ground, and always follows the shortest path, so unless the fish are between one of those two combinations, the electricity will likely not travel through them. If your heater is in your display tank, it's more likely a fish will end up between the wires (I.E. "in circuit").
AW2 is right. Always buy Titanium. 0% chance of breakage.
... and while you are at it, buy two. Even if the second one is glass, you can keep it on the shelf for emergency failures, quarantines, water changes, etc. As cheap as they are, there is no excuse not to.
I run two heaters on my system, both Won titanium heaters. One is set to 78, the other to 74. If the first one stops working for whatever reason, the tank will cool to 74 and the other one will kick in as sort of a "failover."