Hoping someone could give me some solid advise on where to place a bulkhead to link two 20 gallon tanks together. I purchased a fiji cube DIY sump baffle kit for a 20 gallon long with the plans of using this under the display. I have since purchased a roller matt which is going to make my refugium area much smaller than I would like. I have decided to move my sump into my basement and purchase a second 20 gallon tank. the first will be for a roller mat and skimmer and the second will be my refugium and return. My question is how to best link these tanks together? Should i place the bulkhead near the bottom and place the tanks siode by side? or raise the bulk head up to get desired skimmer level and put the second tank below the first (one on top of the other)?
Please, any advise would be much appreciated.
Please, any advise would be much appreciated.

