Fish freek said: A replacment membrane should run you about $70 for a 50GPD and $85 for 100GPD.
Yeow! Shop around and you'll find prices half that for Filmtec membranes.
Fish freek said: RO
water is as pure as your gonna get.
Well, sort of. Within the limits of our hobby, water that goes through a DI
(Deionization) unit is "cleaner" than water passing through a RO
membrane. Think of an RO
membrane like a VERY effective filter, and a DI
resin as a polisher to remove most of the remaining contaminants.
Swish - As far as which units to buy - I always catch myself thinking "if I only knew then (when I was thinking about buying my first RO
unit) whaat I know now..."
Prices are all over the board from different suppliers. A few things you want to consider:
What brand name of RO
membrane is included, and what's the rejection rate.
What is the gpd rating of the membrane?
What are the pore sizes on the sediment and carbon block cartridges?
If you're getting a DI
unit - is the resin color-changing? If not, get a TDS
meter as well. And on this issue - you should get a TDS
meter regardless. I routinely run weeks and weeks of water through my DI
resin after it starts changing color. You'd be wasting money if you threw it out when it starts changing color.
Do you have any unique issues in your tap water that require special treatment?
Look at a pic of the unit - better units don't have lot's of tubings going everywhere - they are efficiently plumbed without lots of tubing.
Does the unit hve clear housings? Lots of people prefer these.
Does the unit come with a pressure guage?
I hear lots of mixed experience with TDS
meters that come on the units.
Does it come with a flush valve?
Does it include an auto shut-off?
If you want to use it for drinking water too, you'll have some other equipment/issues to be concerned with.
Off the top of my head - these are the things I would think about.