Counter Current Protein Skimmers
Counter current protein skimmers force water to fight an opposing current, which greatly slows bubbles' advancement through the chamber, allowing them to collect more waste. Higher-tech innovations have come along since, but counter current protein skimmers remain inexpensive and effective, particularly in smaller tanks. You will need an air pump and airstones (usually limewood) to power these skimmers. Buy the tallest you can afford for the best results.