I own both a 200W and 300W hydor inline heaters. My tanks stay a constant temperature, insanely consistent. Temperature variations throughout the tank are negligible. You can hear them click on and off sometimes, but that's basically the only con I can find in a long list of pros. At least it doesn't sit on the back of the tank and flicker... can't stand that.
Overall, it's the best heater I've ever owned and would recommend them without a second thought.
I have a 300 watt one on my 84 gallon. It seems to turn off and on quite a bit so i think a 200 watt probably would have been a better choice. The click is also quite loud when it turns on and off but this may be more noticeable to me since it's in my bedroom. Also the heater is set on 25 and it keeps the tank from 25.1 - 25.3. The temperature dial is also quite loose so an accidental knock could send the temperature skyrocketing. But other then that, I'm quite happy with it. No ugly heater in the tank and no need to get your hands wet when adjusting temperature.
there seems to be several different technologies out there these days...
1) the traditional ceramic core/metal resistor coils and glass heater
2) the titanium heaters (no fear of glass breakage due to temp shock in/out of water)
3) polymer sheeting w/ heating ink (hydor's product)... not sure what this is exactly, but looks similar to solar panels in some respect.
aside from the on/off clicks from the hydor heaters (most noticeable complaint), are there other noticeable differences? the consensus seems to be positive. definitely something i would consider. thanks for the helpful comments.
The only issue I suspect - but have no evidence of - is that the Hydor ETHs can only raise the aquarium temperature at maxmimum 10 degrees F above the ambient temperature of the room. If you have an aquarium in a basement or garage which gets very cold during the winter, you might consider getting a heavy duty, work-horse, in-tank heater.
I have one of the 300W models on my 65, running for only a month. It's very nice so far, exactly what I hoped it would be. The temperature stays rock solid in a 65 degree room at a setting of 76 degrees. I will raise it some just to see what it is able to do.
I suspect the esthetic advantage of this product would not be so important to a tank in a garage or basement, so might not be much of a disadvantage.
if the external hydor can only raise the temp by 10 deg F above ambient room temp, then it really isn't that great of a heater, is it? it seems to me that the heater should be able to raise it to the temp you want regardless of ambient room temp. i suppose all heaters are affected in some way by room temp tho, since winter time brings temps way down in some areas and requires heaters to work harder to maintain temp. i guess it's lucky for me that i live in the sf bay area, where temps are generally mild, even in winter.
still, consensus is in favor, so must be a pretty good design.
It's going to be a function of the power rating. My 300W Hydor is doing fine now at 78 deg. (13 above ambient on a 65g with about 53g of water and the rest hardscape. It is not even breaking a sweat, which is what I would expect. If it did anything else, I would be dissing it as a lousy product. If I put it on a 300g tank I don't expect it to maintain 13deg above ambient. That's too much tank. Really, to specify correctly it is necessary to include the size of the tank that's being heated. I used a 300W titanium on a 30g in my unheated garage last year during the dead of winter. I placed the tank on a laminated 3"-thick maple workbench top and covered the sides with cut up styrofoam sheet insulation. The heater ran almost constantly to keep the tank warm. Ambient temp had to be in the neighborhood of 50 or so degrees below the tank setting at least part of the time. That heater is capable of frying a 30g inside.
Actually, here's some justification for you, Andrew. If you had said C instead of F, your delta T of 10 degrees would have been spot on the spec for the 300W. That's what the owner's manual calls out- 10C (for 48-66gal.)
Novel concept, checking the owner's manual. I'll try to remember that in the future...
I have an ETH200 on my 26G and it was fine while the tank was in the house. Moving the tank to the garage here in Southern CA necessitated another heater--an Ebo Jager 100.
With both heaters I still can't keep the aquarium at a higher temperature than 74-76F with the outside temp in the high 40'sF @ night even with the addition of syrofoam insulation on 3 sides of the aquarium.
The ETH does click rather loudly when turning on as mentioned earlier in this thread.
I have mine mounted horizontally. I sometimes wonder if it'd be more effective mounted vertically.