RODI Help

[bacon5]

Ok so my outlet for my RODI unit is at 33ppm. Tap is at ~250. What filters should I replace? I bought it used with replaced filters, but not a new membrane. The DI beads have been replaced and are still looking blue (I have the color changing ones that go from blue to tan). The membrane is 1.5 years old and the filters are 1 year old. I would say that the unit has not been heavily used since I only have a 20 gallon tank.

Thanks for any help

[mcgyvr]

How long has it been running for when you did this test and was it just installed/put into service..
The output will be high initially (up to a minute or so after you just start flowing water) but will drop quickly..
And even longer if you just set it up..

The output after the DI stage should be 0.. (1 or 2,etc.. is probably fine but many replace it as soon as TDS is 1)
The output after the RO membrane (before the DI) should be a 93-98% rejection ratio from tap (depending on brand,etc..)
RO membranes "should" last roughly 3-5 years.
Having a 40G tank I replace all the regular (carbon/sediment/DI) yearly and should probably be doing it more often..
But my Xmas gift to myself is always new filters each year..

Hope that helped..

[Opus123]

+1 on Mcgyvr's advice. It sounds like your membrane may be shot. If you got it used no telling how old the membrane was or how they took care of it. At tap of 250 you should be looking at a TDS of 10 or lower after the RO membrane. This will also save you money on DI refills. At your current rate of 33, your DI will last around 135gals before it is exhausted. Get a new membrane with a rejection rate of 96% and you are looking at a TDS of 10 after the membrane and you will get around 445gals out of your DI. Buy a Spectrapure 99% rejection rate membrane and your TDS should be around 3 and you will get around 1400gals out of your DI.

Also, I don't really trust the color changing DI. Mine will change colors but I will still get several months of 0 TDS out of it.

[Vinny Kreyling]

William,
RO units run better the longer they work. Hopefully you use a top off container for all your water uses including changes. They also build up "nasties" on the membrane while in use so a flush kit would be a wise investment. As has been stated a complete change of filters & a new membrane are the wise choice here. The better the rejection rate of the membrane the better for you. Personally I use Spectrapure but any of the sponsors here on RC will do right by you.

[rillaboratories]

+1 spectrapure

[Opus123]

I disagree on the flush kit. They do very little at a consumer level. Now a kit to divert the first minute or 2 of RO water from the DI is a good investment.

[outssider]

+1

this is excellent advice......everyone should be doing this..... and it's easy to do too

[dt204]

OP, sounds like you should start from scratch with all your filters. No telling what they may have been through.
I too have been burning through DI. My tap is testing 400. Ro is putting out 100. Just changed my DI resin today. I just changed the membrane 6 months ago, and the prefilters a month ago. My membrane must be shot?! I'm not sure what's going on.
I recently purchased a new rental property, and it has a water softener that is no longer being used. I'm planning to hook it up before my RODI to help with longevity of my filters.
Also hoping to get a 99% membrane this time

Sent from my Pixel XL using Tapatalk

[Orm Embar]

You could also test your TDS after the RO but before the DI to see what your TDS is and calculate your membrane efficiency (there are equations for this, and at least one online calculator). If your RO efficiency is less than 95% then you may want a new membrane. You can then figure out if you need a new DI resin once the RO membrane is replaced (if bad).

Having said that, if you're getting 33 TDS after the RO and DI resin with 250 TDS tap water, your membrane efficiency is less than 90% regardless of whether or not your DI resin is working. Therefore, you need a new RO membrane. If your post-RO but pre-DI TDS is really high, you may not need new resin but my guess is that you will need new DI resin as well.

By comparison, I am running a new SpectraPure RO/DI unit; tap TDS is 75, post-RO and pre-DI is 0-1 TDS, and post-DI is 0 TDS.

[cpballer]

Originally Posted by Opus123

+1 on Mcgyvr's advice. It sounds like your membrane may be shot. If you got it used no telling how old the membrane was or how they took care of it. At tap of 250 you should be looking at a TDS of 10 or lower after the RO membrane. This will also save you money on DI refills. At your current rate of 33, your DI will last around 135gals before it is exhausted. Get a new membrane with a rejection rate of 96% and you are looking at a TDS of 10 after the membrane and you will get around 445gals out of your DI. Buy a Spectrapure 99% rejection rate membrane and your TDS should be around 3 and you will get around 1400gals out of your DI.

Also, I don't really trust the color changing DI. Mine will change colors but I will still get several months of 0 TDS out of it.

What would be the waste to clean water ratio be? If you go 1:1 that wouldnt bring the ro tds down right compared to if u go 2:1 or 3:1?