If this is the same filter unit I bought, you shouldn't need a replacement cartridge. The one used is reusable. All you need do is take it out and clean it. Be careful not to damage it. If a replacement is needed you should be able to obtain one from Home Depot, or contact the manufacturer.
Picture is upside down. Water enters one 1-1/2 port and exits on the side oposite. Water is guided through the filter which traps debris. The red valve is at the BOTTOM of the filter and is used to blow out larger pieces of debris. The clear plastic case unscrews from the white plastic pipe connection and the stainless steel filter can be washed to remove small debris. We use these in outdoor fountains.
More like 4 gallons a second. We use these in outdoor fountains.
I think you can use it after changing filter to bigger one. But there are cost effective way to do the same and this device is expensive.
We run this on a filter system coming from a pond going to a 40 psi residential sprinkler system. Not sure the gpm or gph but it a lot.
The unit I bought has a washable/reusable micro filter element. Not sure about the one you bought? If it says to replace filter, then it should have a quide/chart to give the user some idea as to when to replace. Of course, it really depends on the amount of sediment and impurities found in your water as to how long a replaceable filter will last. As a last resort, if you see a noticeable drop in water pressure, or out put at the tap, you might consider replacing. I usually pull mine out, clean and reinstall about every 3 months, due to the sediment and iron in our water. Bo