Wet/dry sumps do nothing to reduce or remove nitrate. In fact... bio balls create nitrate. A bacteria that lives on the bio balls consumes ammonia, and converts it to nitrite. Another bacteria on the bio balls consumes nitrite, and converts it to nitrate. Bacteria that consumes nitrate cannot live in an environment that contains oxygen, such as bio balls, filter pads, shallow sand beds, rock rubble, etc.. Large live rock, and deep sand beds with anaerobic (oxygen-free) zones are the only natural places this bacteria can survive. Other than that, something like an Aquaripure filter, external algae scrubber, or nitrate absorbing media, water changes are the best methods of nitrate reduction. A refugium with macro algae and deep sand bed will help. With enough sand, rock, and macro algae, nitrate can be greatly reduced... or completely eliminated. This means far fewer water changes, which adds up to savings by using less salt. I haven't performed a water change in over two months, and I only change water to replenish some of the minor elements that I don't dose. It takes a good bit of time for a biological filtration system to establish enough to sustain itself, but it is absolutely possible. Creating the proper environment is the key...