Aside from the light, you shouldn't have a nem to begin with. 5 months is not long enough to have waited to get one. When it comes to nems, pristine water, and no water fluctuations are a must. These creatures are extremely sensitive to any type of water changes, and will show they are stressed out by always moving around. Nems when comfortable, will find a place to secure their "foot" to, and if it's a good spot, they will stay there. Water fluctuations are a given in any tanks younger than a year. Beneficial bacteria, and the tanks overall ecosystem is still being hardened at these early tank stages. If that nem doesn't die within a few days, it might be a good idea to take it back to where you bought it, or get it under some stronger lights.