Water changes are almost always necessary to replace trace elements in the water, even if you use a denitrator. But i have an electric water pump used for draining swimming pools, big floods. It attaches to a garden hose, so to drain water i'll use the pump, then to replace, ill mix saltwater in a 55 gallon garbage can, take the same pump and use it to pump the new mix from the garbage can back into the pool. Or i might just use a five gallon bucket to scoop it out. Whatevers easier/faster.