Starting up a cold tub we have at work for after workout use. It's 477 gallons has a filter system. Any special considerations for colder (40 degrees) setups? Also, any way to vacuum with water in it? Probably easier to just drain and re-fill when it gets enough sand in it. Its a ColdTub Polar plunge. Piecing together a testing setup from leftovers at home. Will test monday.