Overflow with dual U-tubes
I recently bought a new overflow cup to replace one I had broken and this one came with two slightly smaller U-tubes instead of the single larger one I had before. I got them both set up and everything is working great, except that one of the U-tubes gradually gets more and more air inside it until it loses suction completely.
Could it be because the flow isn't enough that I need both tubes? It seems to be doing fine with just one tube...