if you have 3 stage system this will be Stage 3 - RO-Membrane

if you have 4 stage system this will be Stage 3 - RO-Membrane

if you have 5 stage system this will be Stage 4 - RO-Membrane

• please see the pictures attached to the product and compare it to your system

Aquasky rot 4 - 50 -75 gpd-residential-RO-membrane 

• Semi-permeable stages of pores size 0.0001 microns, which is 620,000 times finer than a human hair,10,000 times smaller than a red blood cell 2,500 times smaller than bacteria And 20 times Smaller than virus.
• 50-100 Gallons / day Output Fastest Flow
• 98% Stabilized Salt Rejection (Minimum Rejection 96%) NSF/ANSI Standard
• Membrane Dimensions: 12.75" Overall Length, 1.85" Diameter (Fits Standard 2.1" ID Membrane Housings) 20 -3/4" / 9.5" 3.5 /11-( 98%) pxi - CVM 

COMPATIBLE WITH

• US Water Reverse Osmosis Water Filters.
• US Water Galaxy Reverse Osmosis Water Filters.
• US Water Aquapurion Reverse Osmosis Water Filters.
• Watts 5 stage Reverse Osmosis Water Filters.
• Purevalue Reverse Osmosis Water Filters.
• Proline Plus Reverse Osmosis Water Filters.
• Proline Gold Reverse Osmosis Water Filters.
• Nelson Reverse Osmosis Water Filters.
• Isopure Reverse Osmosis Water Filters.
• iSpring Reverse Osmosis Water Filters.
• Tier1Reverse Osmosis Water Filters.
• Hydronix Reverse Osmosis Water Filters.
• Max Reverse Osmosis Water Filters.
• AQUARIUM Reverse Osmosis Water Filters.
• APEC Reverse Osmosis Water Filters.
• APEX Reverse Osmosis Water Filters.
• Titan Water Pro Reverse Osmosis Water Filters.
• Home Pure Reverse Osmosis Water Filters.
• Premier Reverse Osmosis Water Filters.
• Blue Wave Water Reverse Osmosis Water Filters.
• COP and all standard 5 stage RO Systems.
• 4 stage ro filter replacement kit.