Yes, you can use Merckens coating. You may need to add some vegetable oil to make it flow. Use this ratio: 1 lb. of melted chocolate + 1 tsp. of oil. Start with 1 tsp. then add another tsp. of oil to the fountain if it isn't flowing smoothly. I hope this helps! 
I own 5 fountains and use them for weddings all the time.
First, I would never use just regular chocolate chips for a fountain. Ever notice how those things still kinda look like choc chips when they are in a cookie that just came out of the oven? When dealing with fountains, you want a chocolate that will actually MELT.
I use the Merkens and merkens only .... microwave them 30-40 seconds at a time. Stir the crap out of it ... then another 30-40 seconds .... stir the crap out of it. I add the oil at the very end .... I've never really measured (I'm a "until it looks right" cook), but it should flow smooth and fast off of the end of a big spoon without having a lot of oil spots in it.
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