Convict goby? I would say skip it and get something else. Convict (engineer) gobys tend to make one burrow and stay in or very close to it so it won't do much to clean sand and such. The only time my engineer leaves the burrow is when I put the turkey baster near to target feed him. Don't get me wrong they are cool but if you want it to clean sand you will be disappointed. I have personally found the orange spot diamond goby to be an awesome sand sifter. Mine is always out churning the sand and eats prepared foods readily. I've also heard dragon gobys are good also. Saltwater dragon goby that is, not the fugly freshwater one of the same name. Something to remember with diamond gobys is they get about 6 inches and are notorious jumpers so you will need a lid. Eggcrate (lighting diffuser) works but best option is transparent screen like BRS sells.