You can add sand but its going to make your tank very cloudy and murky, even after thoroughly rinsing it. I just did this to my tank. I bought play sand from the department store. It took literally almost 2 days for it to finally settle. I did several water changes as well. I had my axolotls in a bucket for the time being. I hear it's better to add the sand first, then use something flat like a dish plate to put at the bottom of the tank, then lightly poor the water on the plate so you don't stir the sand particles.
I don't think it will ruin your cycle, unless you do a lot of water changes without any dechlorinator. Always keep your used filter when doing water changes, if you have one. It has all the healthy bacteria on it. Then, change the filter the next day or so.