I have a vortex one. I bought it on ebay.
It does one hella job of polishing the water. They can be a bear to get started, but after a few times you get the hang of it. LOL first time it pumped my tank full of diatom powder.
The powder starts off sparkling white, and after running it for an hour its totally gungy brown-yellow.
And ya if you get one use the pool filter diatom powder. I happen to have a 50lb bag of it stored in my boiler room.. bring some jars next time and I will give you some.. but be careful with it.. microscopic little jagged sharpies that get in your lungs.