A water change should clear up a lot of the cloudiness in your tank from the sand. I'm not sure how much difference it will make to the plec but if you ever get into bottom feeding fish like corys, they'll love the sand. Gravel can cause barbel erosion whereas fine sand does not. IMO, it's also a lot prettier. Be careful that you don't put too much sand in your tank. Most of the experts recommend a maximum of half an inch. And make sure that you rake the sand when you do water changes. Sand can compact and develop anaerobic pockets that produce hydrogen sulfide gas. If released into the tank, the gas can be fatal to your fish. Raking the sand ensures that all areas get oxygenated.