I run a Hydor-Theo PTC shatterproof glass heater in my Rainbow Lifegard in-line heater module on my 55 gal
tank setup --> http://www.pentairaquatics.com/produ...le_heater.html
. This series of Hydor heaters are unique in that they use a conductive polymer sheet as the heating element instead of a metal coil. The theory is that the peak operating temperature can be lower to still achieve the same amount of heat transfer, since there can be a lot more surface area with a polymer sheet than with a metal coil. This is 'life and death' important if the heater is ever allowed to operate dry (because a metal coil will burn out but the polymer sheet stops getting much hotter and survives). This is a much greater risk factor if the heater is installed in an in-line heater module depending on a pump to flow water past it and force trapped air out of it, versus being immersed inside a tank. For this reason, the Hydor PTC is the only heater that I would ever consider running in external forced flow installations. Since I also run ceramic bio-balls inside my in-line heater module, the lower peak temperature of the Hydor PTC heating element is also a supposed plus in regard to potentially killing off 'good' bacteria if the heater stays on and the water flow stops for some reason.
Hydor of course also offers their own combination heater and in-line module --> http://www.aquatichouse.com/Pumps_fi...20external.asp
--> for a little less money than buying the Hydor-Theo heater and another company's in-line heater module separately, but the Hydor in-line module doesn't have room for adding bio-balls, is harder to take apart and clean, and the 'plumbing' is messier (particularly since I'm running other Rainbow Lifegard filter modules too). However, there are several degrees of error in the knob markings versus the actual tank temperature with my Hydor-Theo (but this might be due to the fact that there is actually a temperature difference of several degrees between the water in my in-line heater module and the water in my tank). Perhaps the Hydor combination unit already 'knows' that it's being used in an in-line application and has been recalibrated for that application, where my Hydor-Theo thinks it's immersed in a tank when it's actually installed in another company's in-line heater module.
Won titanium tube heaters take a different approach, using a metal coil for heat but providing a 'bulletproof' outer tube which cannot crack under any conditions. The Won heater's great claims to fame are that it was the first to use the titanium tube, the first to use a separate temperature sensor which accurately measures water temperature away from the local effects of the heater, and that it uses a control box which (presumeably) switches power to the heater electronically instead of via a 'mechanical' switch contact inside the heater tube thus eliminating another common cause for heater failure. Also ViaAqua now makes a similar titanium tube heater, but (presumeably) doesn't have as sophisticated of a control box. IMHO
the Won is the ultimate heater for inside the tank immersion installations because of the 'bulletproof' tube and super accurate temp control, if you don't mind the extra 'mess' of the separate temperature probe and control box.
In my 6 gal
tank I run a VisiTherm 25 watt conventional glass tube heater. It was very cheap, it's well protected from damage by a 'rubber bumper' which almost totally surrounds the glass tube, and the thermostat setting is actually very accurate. Plus there aren't very many heater companies which offer a 25 watt model for use in very small tanks i.e. the smallest Won heater is a 50 watt. If you're on a tight budget, VisiTherm is 'the cream of the crap' so to speak.
As to Ebo-Jager, I run one of these (which I've had for a couple of years) immersed in the tank as a second heater on my 55 gal
. While these heaters have an excellent reputation and I've certainly gotten great service out of mine, IMHO
recent technological advances have passed them by and I wouldn't buy another one today. The Won titanium or Hydor PTC are in the same premium price range and use better technology for their respective applications. The VisiTherm uses the same technology and is quite a bit cheaper, just as accurate, and better protected from impact damage.