RO/DI TDS numbers ?

O.K.

I have a question for the RO/DI gurus.

I have just changed my filters and DI resin with replacements from BRS.
In order:

1 - 5 Micron Premium Depth Sediment Filter ROsave.Zs
1 - 5 Micron Purtrex sediment filter
1 - MATRIKX + CTO®/2 Carbon Block (5 micron)
1 - MATRIKX® +1 Carbon Block (1 micron)
1 - 75 GPD Dow Filmtec RO Membrane (6 months old ?)
1 - Color changing DI Resin

Monitoring @ 4 points with 2 - Dual Inline TDS Meter DM-1 HM Digital:

1st "IN" is Tap Water = 280ppm
1st "OUT" is AFTER the 2 - sediment filters and 2 - carbon blocks (just before the membrane) = 272ppm
2nd "IN" is After the membrane (before the DI resin) = 16ppm
2nd "OUT" is final product water = 0ppm

My question is that there is only a 8ppm reduction after the sediment filters AND carbon blocks .... is this normal?

Also the membrane is only rejecting ~94%.

Just didn't look right to me even though the final product is 0ppm.

What do you think?

 

Yes. Sediment filters and carbon blocks are for removing suspended solids, not dissolved solids.

You would be better off (and less expensive) if you went with a 1 micron sediment filter and the MATRIKX +1 carbon block (.6 micron). That's all you would need, and it would save you money as you would only be replacing 2 filters (not 4).

94% rejection rate is probably because your water pressure is a little low. Get the psi up to a steady 65psi and you would see the rejection rate up around 98%.

 

Hmm ..
Thanks, makes sense to me - suspended solids/dissolved solids.
I guess I was expecting to see a drop in the TDS.

And I did, in fact, suspect that my water pressure might be a bit low ... time for a pressure gauge to check.

Since I just replaced the filters - I will keep this info in mind for the next change in 6 months and just go with the 1 micron sediment filter and the .6 micron MATRIKX +1 carbon block.

Thanks for the quick reply.

 

Why did yopu buy all those 5 micron sizes? 1 micron or less is much preferred and will work much better with longer filter life meaning a lower cost of ownership.

I would highly recommend the following arrangement for best carbon block and membrane life.
1. One 1 or 0.5 micron absolute rated prefilter. Absolute is much better than the normal nominal rated filter.
2. One 0.5 or 0.6 micron Matrikx +1 Chlorine Guzzler 20,000 gallon carbon block
3. A new RO membrane since yours is only operating at 94% efficiency (272 in and 16 out)
4. A full size 20 oz refillable 10" vertical DI.

The 5 micron prefilter will not do a good job of protecting the more expensive and more important carbon block so the billions of tiny pores can become clogged rendering it useless for chlorine adsorption. The 5 micron carbon block is only good for up to about 9,000 total gallons of normally chlorinated water while a 0.5 or 0.6 micron can do up to 20,000 gallons and protect the membrane better making it last much longer.

Prefilters and carbons protect the membrane from suspended solids 10 microns up to visible with the naked eye)or big stuff and chlorine. the membrane and DI remove TDS, dissolved solids (0.0001 microns and smaller). Suspended solids do not register on a TDS meter, they show up as turbidity or particles.

Replace the membrane. Did you know, for every 2% you increase the membrane efficiency you can DOUBLE the life of your DI resin? Imaginge going to 98+% efficiency. My Spectrapure membrane is averaging 99.35% efficiency even after almost 3 years of heavy use and my DI cartridges last over a year at 0 TDS. There really is a difference and you can get them on sale here:
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Always make sure your prefilter is the same micron size or smaller than the carbon block so it protects it so a 0.5 micron prefilter for a 0.5 or 0.6 micron carbon etc. I actually use a 0.2 absolute micron prefilter and get better filtration, longer filter life since its pleated and has 10x the surface area and less pressure drop than with a 0.5 or 1.0 micron.