New fiddler crab

[Ashley Henderson]

My son brought home a fiddler crab after a trip to the pet store with his grandmother. This was unexpected since the trip was for his sister to get more fish for her tank. I set up our extra 10 gallon tank as best I could with the materials I had on hand. After talking to the pet store they informed me that the crab would do fine with freshwater and gravel. After some online research I found out that guy is an idiot. About $45 later we have marine salt, dechlorinator, sand, blood worms and a filter for the little guy. Here's where my questions come in. All they had in stock was crayola play sand in colors, we chose blue and I rinsed the sand before use to make sure it wouldn't tint the water and hurt Ron. Is the sand safe? I could find nothing online about using colored play sand. After installing the filter I noticed a few hours later that the water has a layer of foam on the top, swirling my finger in it breaks it up but I don't know if it's safe for Ron. Ron crab has also been hiding in the water in the corner of the tank for hours, when I get close to him he moves, but I don't want to mess with him too much in case he is molting. We're just guessing at his sex since he only has one full claw, the other looks to be growing in, and one leg is missing. I actually like the little guy and don't want him to die. I'm having a hard time finding budget friendly filters (using their mamaw's big one for the time being) that don't need a high water level to work. Also same problem with a water heater. Any help or tips would be greatly appreciated. Remember I had this crab thrust upon me and I'm doing the best I can until school starts back up and I get regular paychecks again.