Metal Trap MTU25 Pre-Filters - Water Up to 25,000 Gallon MTU25 pre-filters up to 25,000 gallons Pre-Filters Stain-Causing Metals Before Having a Chance to Damage Your Pool or Spa. Traps Iron and Copper from Municipal and Well-Water Sources During Fills and Top Offs. Incorporates New "Filtration Media Materials" to Trap Metals. Easy to Use! Just Attach to Hose, Flush and Start Filling.