RO / DI units

You need to be very careful when buying 100 GPD membranes. The largest manufacturer in the residential size membranes is Dow Filmtec and their 75 GPD is the standard of the industry used by most reputable vendors. On the flip side their 100 GPD membrane is not even a true RO membrane and is only 90% rejection rate so is classified by the ANSI/NSF as "Pool and Spa Use" not designed for drinking water applications. The 75 on the other hand is 96-98% rejection and rated for drinking water use. GE Water makes a 100 GPD membrane which is almost identical to the Dow 75 in all respects, they just advertice it a little differently. Dow Filmtec says 75 GPD at 77 degrees F and 50 psi. GE says 100 GPD at 65 psi and 77 degrees F. Lay the two graphs or curves on top of each other and you see they both do 75 GPD at 50 psi, 90 GPD at 60 psi and 100 GPD at 65 psi, and both at asustained 96-98% rejection.
Do not buy a system with the Dow 100 or you will go through DI like crazy.

There is a 150 GPD membrane on the market and I used to have one. The problem is its not very reliable and places like Spectrapure found in testing they could not get enough to meet their strict standards of better than 98% rejection. They must have found a few though as they are selling them in a reef quality RO/DI system this month for $150 with a batch tested version of the 150 membrane. Pretty good deal.

Another option to get over 100 GPD from a 75 GPD membrane is an Aquatec 8800 booster pump. I can get 125-150 GPD at 90-100 psi on my booster pump and at 99.4% rejection since membranes work better at higher pressures.

There really is no down side to higher GPD systems as they have the same waste ratio, the same rejection rate and the same physical size if they are a single membrane system and cost no more and often less than some brands 15-25 or 50-60 GPD systems.

 

i would listen to him. i posted a thread about this not long ago and after he told me about Spectrapure i did my own research and found it to be the best. im getting their maxpure mpdi 40gpd system and it still stayed int he budget that my wife set. i would just pay the extra money and have peace of mind.

 

Vern don't get the 40, it takes too long to make the same quality water as the 90 GPD version at the same cost. Why wait over twice as long for a bucket of water when the cost and quality are the same, you time is worth something.

 

that is true. ok ill get the 90gpd i wasnt sure if it would use the filters up any faster or not. but i guess the filters only go as fast as you use them

 

No everything lasts the same. You are only making x gallons per day regardless of the membrane size, the 90 just makes it much faster.

 

I found a bargain on a Vertex 100GPD RO/DI unit, I have heard they perform very well but they over-run the membranes causing constant replacement.

Anyone have a review on this item?

 

Very poor design. They tried to reduce the waste ratio which is not a good idea. All membranes must be flushed, there is no getting around it. When you reduce the waste ratio the solids build up on the membrane fabric and it fouls prematurely. The best thing you can do is get a capillary tube flow restrictor for $5 and trim it for a 3 or 4-1 waste ratio so you don't ruin the membrane.

I don't see Vertex units being around for long as they have a well deserved bad reputation. Enough dissatisfied customers complain and they will go out of business as far as treatment anyway. There have been a couple others attempt this in years past and most are no longer around.