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Indiana Reefin
07/10/2012, 07:18 AM
I have well water and a rodi unit. I am getting a reading of 546 from my tap and 17 from my filtered water. That is right at 98% rejection rate. I do think I am due for a new RO membrane. Do you think this is what I should expect? Just replaced the di resin and carbon filter. I need to get a new sediment filter and possibly a new membrane. The membrane is around 2 to3 years old. If you guys and gals could give me input that would be great! This is for clownfish and an a anemone.

Entropy
07/10/2012, 07:37 AM
546 is pretty high for source water. Your membrane is probably shot after 2-3 years. 17ppm is actually not terrible if you are not keeping corals, but it is going to get worse. Also have you seen a drop off in the production rate of your RO unit? If the membrane is going it should be making less water (more waste water).

Indiana Reefin
07/10/2012, 07:50 AM
Production has gone down. I need to get a new membrane and pressure gauge

firebirdude
07/10/2012, 08:35 AM
I think you know the answer to your question...

Vanquishxxxx
07/10/2012, 10:29 AM
Def membrane, with those high readings, suprised it lasted this long.

Indiana Reefin
07/10/2012, 10:41 AM
Thanks for all the help the only reason I asked is because I am getting a 97% rejection rate. Will it get a lot better with a new membrane?

firebirdude
07/10/2012, 11:36 AM
You're getting 97% when starting with a rather high number of 546 AND brand new carbon and DI resin. The fact your production has decreased is a dead giveaway that the membrane is toast. With a dirty membrane, your new carbon and DI resin are working overtime. I'd replace the membrane ASAP.

And, as has been said, your source water is pretty high. I'd think about adding a stage or two to your RO/DI setup. Maybe dual membrane.

Indiana Reefin
07/10/2012, 11:51 AM
Would dual carbon or dual sediment filters help alongside with dual membranes?

firebirdude
07/10/2012, 11:55 AM
Anything can only help. Think I'd run dual DI resins before dual sediment filters, but anything will help.

I'd think about something like this (http://www.airwaterice.com/product/1NEPTUNE/NEPTUNE-200GPD-RODI-With-2-Membranes-3-DI-Cartridges.html). AW&I is local to me and I've met the owners several times. Placed two orders as well. Great people with great customer service...and RIDICULOUSLY fast shipping. I obviously don't live far away, but I had both my orders on my doorstep IN UNDER 24 HOURS. My local reef club gets a discount through them as well.

Buckeye Hydro
07/10/2012, 01:24 PM
Let's back up a minute folks. There's some not quite correct info in this thread...

The two most common signs of a membrane gone bad are 1) poor rejection (you are at 97% so you are doing fine here), and 2) slowed (normalized) production.

You can't tell if a membrane has gone bad just by looking at the permeate TDS. You have to calculate the rejection rate.
97% rejection w/ feedwater @ 55 ppm = 2 ppm
take the same perfectly good membrane and feed to 860 ppm water and you'll see a permeate TDS of over 26 ppm.

The most common cause of slowed production is not a bad membrane - it's clogged prefilters.

The OP doesn't have a pressure gauge - that's where I'd start. Install a pressure gague kit - the gauge should read AFTER the prefilters and before the membrane - that way the gauge is exposed to the exact same pressure as the membrane.

Russ

Buckeye Hydro
07/10/2012, 01:27 PM
Thanks for all the help the only reason I asked is because I am getting a 97% rejection rate. Will it get a lot better with a new membrane?

No - not a lot better. And you may not even get 97%. We have 75 gpd membranes that we test for rejection - that's about as good as you're going to get in terms of making sure you get a high rejection membrane.

Russ

Indiana Reefin
07/10/2012, 02:00 PM
No - not a lot better. And you may not even get 97%. We have 75 gpd membranes that we test for rejection - that's about as good as you're going to get in terms of making sure you get a high rejection membrane.

Russ

Thanks Russ. That's what I thought. Do you think 17 is okay for fish?
What about corals? Everyone always shoots for 0. Seems unlikely for me.

Buckeye Hydro
07/10/2012, 02:20 PM
The textbook answer: There's no telling because we don't know what is in the 17 ppm.

More practical answer: Yes - there's a high likelihood you'll be fine in terms of the fish surviving. You may be inviting algae issues.

If you are going to have corals, run that 17 ppm water through a larger than normal DI bed and get it down to 0 ppm.

Russ

Indiana Reefin
07/10/2012, 03:28 PM
Well good news is I added another container of di resin and it dropped down to 11 ppm. Pretty good from 546. I would have to probably add 2 to 3 more stages of do resin and who knows how long they will last before the di resin exhausts. it could cost me a lot of $.