I'm new to the group, in the process of setting up a 75g tank. Does anyone here have experience with substrate heaters such as Red Sea's Root Therm. Do they really work? Are they worth the $$? Do they increase the water temp?
I have the Hydor Hydrokable system which is a heathing cable and thermometer controller system. There are many debates of the benefits of a heating cable system, but in the end it is inclusive that they in no way hurt a planted tank. There seems to be some evidence that where they shine is in the long term use say 3-5 years running in an established tank. If plants "grow" any better if up for debate but i believe the benefit of having water circulate throughout the substrate is very beneficial for many reasons.
What i have found from using the Hydor system is it might not be suficient to heat your entire tank with just the undergravel heating cable. I have this system in a 26 gallon tank and now that it has started to cool down, it can't keep the temp at 82 degrees when the room temp goes below 65 degrees. I left the windows open tonight and when i came back the room was 59 degrees and my tank was down around 78. I installed a small 50 watt heater to fix this for now. For most of the year i will not need a second heater, and actually the heat is not turned on yet, but as long house stays within 20 degrees of where i want to keep the tank, i don't believe it will be a problem.
I installed the 50 watt cable which is rated for a tank size between 16-35 gallons, and i really couldn't have went bigger due to the fact the cable would be too long to use across the bottom of the tank. If you decide to use the heating cable system, you will need to use another heater, say a hydor inline setup, and you would have more than suficient heating for your tanksize. The 100 watt cable will fit your tank, and you could also turn the inline heater off for most of the year if this will keep your tank up to temperture. http://www.drsfostersmith.com/product/prod_display.cfm?pcatid=11371