I currently have a Emerald 26 sump, and there is a large opening shaped like a fish between the skimmer section and the refugium section. What are some ideas of what to use to block that hole while still allowing water to pass through? I have tried egg crate but the holes are still too large and let smaller hermits and snails get through. I am trying to keep the inverts from the refugium out of my skimmer section. Thanks in advance!