I need an aquarium heater that is suitable for a 15g tank and is completely invisible from view, nothing can show as it will be on display in my parents house. I don't care how much it costs. I have heavily researched this (going on 5 hours non-stop now) but have yet to find 1 with a high enough wattage. No equipment can show inside this tank. That's why I'm custom ordering an internal filter built inside the frame of a hollow rock that looks good. Do you have any ideas? So far a have a few possibilities, none of which appeal to me.