Shouldn't my 75 GPD RO membrane remove 99% of TDS?

[randyBRS]

100gpd membranes usually aren't as efficient as a 75gpd membrane but getting a TDS of 49 from a Tap with a TDS of 350 is well beyond the normal drop in 100gpd efficiency. Even if say the temp was really cold and the pressure really low one should still expect over 90% rejection from a membrane with very slow production and at some point wont produce at all.

Great point! There still should be a reasonable expectation of rejection rate for a 100gpd membrane that doesn't really fit with @jeff williams reported numbers. Especially if that membrane is a DOW! It's pretty hard to speculate further causes without some more info.

-Randy

 

[randyBRS]

This is one of my favorite tests Ryan did on pressure as it relates to rejection rate and water production!





-Randy

 

[Squid]

In NH my TDS right out of the tap is 3tds. Would it be a problem if I just took my water stright from the tap for my tank? Or should I keep running it threw my RO/DI system first?

Wow nice, you would definitely be fine topping off your tank, but for how long until you start getting some algae idk.

 

[jason2459]

In NH my TDS right out of the tap is 3tds. Would it be a problem if I just took my water stright from the tap for my tank? Or should I keep running it threw my RO/DI system first?

It all depends on what's in the the water. TDS numbers do not indicate quality at all as it doesn't say what's actually in the water. Some people have used straight tap water for many many years and just treat it for chlorine. A TDS of 100 could potentially be just fine for a tank where as a TDS of 1 could kill.

Like in my case I have old copper lines and I know I have a high copper content in my tap. This would be very bad for my tank. The other thing about always using RODI is that you never know when your water supply is specially treated, "flushed", or end up in a boil order. Just look at Flint.