I just discovered the Jaubert method and its implicit simplicity. I have old undergravel filters for 15 gallon tanks I don't use but it looks like I was right in the decision to save them. I can use them as my plenum in a 20 gallon tank. Now the challange is to figure out where I can put a 20 gallon. It is so much simpler than the berlin method. If I ever do a large reef tank I will combine the Berlin overflow method wiith the Jaubert gravel/sand method in the refugium... but that is a pipe dream. The beuaty of this is one can alternate the lights. Main tank light on in the day and refugium light at night for stable oxegen levels.