It's a "hardness" test kit. All the major manufacturers make one, or you can buy online. Just be sure you get the one with two reagents, one for GH and one for KH -- don't ever buy the strips.
Is it possible you contaminated your tank? It looks to me like some type of fungus. I usually soak tank decor in a bucket for a couple of days before placing them into the tank. Did you mention the tank has only been set up for 3 days? An established culture(healthy bactirial action)in my opinion is enough to kill a small amout of fungus. I would do an ammonia flush...