This is what I am doing when my 300 gallon is rebuilt. They are about $45 but worth it because you can hard plumb to the module itself, they switch out heater watt sizes up or down/ replace easily. They are 1" in/out already with no DIY.
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http://www.google.com/products/cata...=xAv6TsvxK6SkiQLhxv2zDg&sqi=2&ved=0CGwQ8wIwAg#
You can finding 1" reducer to 5/8 inch to run the hydor. However I think your fx5 flow might be too fast for an inline heater therefore loosing efficiency.
I like the looks of that one...so you supply the heater and it hooks to that somehow I gather.
If you get the Lifegard Get at least the double module as the single module only really fits 12 inches oh heater. (more like 11.5)