I have no CUC. No need for one at this moment. No algae problem, the diatom I did have. I manually removed. Until, I have a need for one. I will manage without one. Don't get me wrong, they can help with your problem. But, that was not the original question. You did ask how long will it last. People have their reason for what they think is essential to keeping a reef tank. Some say, you must have a skimmer and sump. No, these are not essential. They are nice to have, but you can accomplish the same thing without one. So, let me clear myself here. Unless, you have the food source to support a CUC. Why waste good livestock (dead snails). I rather feed my fish, no more than whAt they need. I have no leftover food laying around. I do weekly water changes to rid the tank of poop and other nasties. I keep a clean house, so why hire a maid.