So what's everyone's Tap TDS and how do you handle it?

[mch1984]

@JoshH has already seen this on my build but I'll comment on here with it. I run around 1200 out of the tap running a 4 stage RO and three stages of DI at 35-40 psi. I want a booster pump but BRS has been out of them for almost two months now. After the RO i'm at about 40 TDS. I'm still on my first round of DI resin, so I'm not sure how long it's going to last.

 

[chipmunkofdoom2]

@DLHDesign it's not true that 1:1.5 - 1:2 is an acceptable product to waste ratio for dual membrane setups. At the very least, the product to waste water still needs to be 1:4 (one gallon of permeate, four gallons of brine), regardless of how many membranes you run. If you have 1 gallon of permeate and only 2 gallons of brine, at least one (or maybe both) of your membranes had to deal with a less than ideal product to waste ratio. There's no getting around that math. If any given membrane(s) produce one gallon of permeate, four gallons of brine need to be going down the drain to keep the membrane clean.

Your goals and motivations are your own, and I cannot question them. My quarrel is not with you personally, it's with the tendency of hobbyists, without reason or explanation, to say "get a booster pump" and "higher PSI is better." If booster pumps were free, I would recommend that everyone with under 100 PSI install one. However, they're not free. In cases where water demand is unusually high, tap water TDS is unusually high, source water is unusually cold, or any combination of these or other factors, the cost of excess waste water or DI resin used might mean a booster pump makes sense financially. As I also said in my previous post, in your specific case, a booster pump seems to make sense because of your tap water's TDS. However, for most people with 5o PSI or greater coming out of their tap, booster pumps are unnecessary.

I did not contradict myself with my last statement. I took issue with your recommendation of a booster pump based on source water temperature alone. Buying a booster pump for the express purpose of getting 10 or 20 gallons more per day does not seem like a wise use of money to me. That was the point of that paragraph. The only reason I brought up TDS is because we are discussing a very nuanced subject and we would do ourselves a disservice by leaving out detail. A booster pump will likely produce lower-TDS water, regardless of source temperature, although that is not always the case. You did not mention this at all as a motivation for buying a booster pump in your first post, which is why I brought it up.

 

[DLHDesign]

If you have 1 gallon of permeate and only 2 gallons of brine, at least one (or maybe both) of your membranes had to deal with a less than ideal product to waste ratio.

This is where the caveat of "if your starting water isn't too high" comes into play. The math is covered in the video I linked to, but basically it works like this;
The tap water enters at some level (call it 100 TDS for easy math). The waste water out of the first membrane is concentrated as a result of the filtering. If we assume a "perfect" 1:4 ratio, then the waste TDS should be around 125 (and assuming a 98% rejection rate, a product TDS of around 2). This waste water is fed into the second membrane. 125 TDS is within the range at which the membrane is functional, so it does the same concentration, resulting in an exit TDS of around 156 (with a product TDS around 2.5). Averaging the two product flows together, we end up with a final product TDS of around 2.25.
If, however, your product water starts high (such as some of the poor people above - 1200?!? - I feel for you; one and all!), then a dual membrane would be a bad idea. If you start at 1200 TDS, the waste from a single membrane will be upwards of 1500 - which is way beyond what the membrane is designed to handle. I think @mch1984 has the right idea in that situation - single membrane with a deep DI stack. It might even be worth adding some more pre-filters (extra floss and/or carbon chambers), though that's really hard to say without knowing what that 1200 TDS is made up of...

In terms of the volume, both membranes were producing product water at that 1:4 ratio. It we assume 4gal in, the first membrane would yield 1gal of product and 3gal of waste. The second membrane would be provided 3 gal, and yield .75gal of product and 2.25gal of waste. Adding those together, we get 1.75gal of product to 2.25gal of waste. Obviously we aren't dealing with straight volumes like this - we're dealing with flow and a pressurized system; I'm just using simpler concepts to illustrate the idea of the increased product water yield that dual membranes in series produces. More specific numbers pertaining to a pressurized system can be found in the BRS video (around the 7:46 mark).

My quarrel is not with you personally, it's with the tendency of hobbyists, without reason or explanation, to say "get a booster pump" and "higher PSI is better."

Oh - no worries; I enjoy the conversation.
I agree with you - booster pumps are not some kind of magic solution to RO/DI system performance. They can help to solve certain situations - other times they are a total waste of money.

However, for most people with 5o PSI or greater coming out of their tap, booster pumps are unnecessary.

If we assume that most people are running a single membrane (and that's a fairly safe assumption I feel) - I totally agree!

I took issue with your recommendation of a booster pump based on source water temperature alone.

Oh - sorry; yeah - I did not mean to imply that. I apologize for giving that impression.
To be more clear; I bought my booster pump after I bought and installed my dual membrane setup. My base pressure is often around 50PSI - which was okay for a single membrane, but did not produce acceptable results with two. I found at that PSI that my ratio was not much different from a single membrane and that my product TDS was high (burning through my DI resin). Rather than give up on the dual setup, I added the booster pump (along with an auto-flush - which certainly helps to keep the membranes clean). Ever since, I've been getting results similar to the above. Obviously that was my specific situation and was driven by my goals. To each their own, of course.

 

[mch1984]

That was after advice from here and BRS, I understand more about RO/DI systems now then I ever did before looking into buying this one.

 

[Forsaken77]

Interesting... well a replacement membrane might do the trick, atleast they aren't crazy expensive not sure a clogged membrane would reduce pressure though. I flush down to my 1-2 range before switching over to DI myself but that's to meet what I know it's usual output is."/

Oh, no I flush down to 7 tds after using it and shutting off the water. Before switching to the DI I go down to 3.

 

[FartyParty]

Im in socal and get around 275tds tap, then use the BRS 5 stage to decrease it to 15, then use dual DI resin canisters to get to zero. I run triton with the apex ato so i just run an ro line direct to the tank and burn through a can of resin every two or three months. it slowly burns down the second di can while my order is in the mail. i do split the ro line for cooking and drinking water just before the di cans, so the carbon/membrane probably depletes faster than most users.

 

[Opus]

@JoshH has already seen this on my build but I'll comment on here with it. I run around 1200 out of the tap running a 4 stage RO and three stages of DI at 35-40 psi. I want a booster pump but BRS has been out of them for almost two months now. After the RO i'm at about 40 TDS. I'm still on my first round of DI resin, so I'm not sure how long it's going to last.

It will be interesting to see what a booster pump does for you. I'm at around 450 tds out of the tap and have a tds of 4 after my spectrapure 99% rejection rate membrane. I use a booster pump but have never installed my pressure gauge to see what pressure I'm currently at. Once I do I plan on running it near 100psi.

As for your after RO tds of 40, you will get about 110 gallons of 0 tds water out of a mixed bed DI cartridge. If you could get your rejection rate to 99% then you would have a tds of 12 and get around 370 gallons out of a DI cartridge.

 

[mch1984]

It will be interesting to see what a booster pump does for you. I'm at around 450 tds out of the tap and have a tds of 4 after my spectrapure 99% rejection rate membrane. I use a booster pump but have never installed my pressure gauge to see what pressure I'm currently at. Once I do I plan on running it near 100psi.

As for your after RO tds of 40, you will get about 110 gallons of 0 tds water out of a mixed bed DI cartridge. If you could get your rejection rate to 99% then you would have a tds of 12 and get around 370 gallons out of a DI cartridge.

That's my goal, to reduce DI resin usage. I should have tracked what I was using a little better after I installed the the ro system initially. Best guess is I've made about 90 gallons of water so far and yes my first canister of DI is starting to get low. The second and third are showing no signs of discoloration so far, but they are getting 0 TDS so that makes sense. I actually got the booster pump and automatic flush valve ordered this morning. So hopefully I will have it installed some time next week. I'll make sure I get some good measurements post RO/pre DI before and after and come back here and let everybody know.

ps. I plan to run around 90 PSI with the booster.

 

[Opus]

A little off topic, but does anyone know what happened to AZDesertRat? He was our resident RO guru and he hasn't been on in almost a year. Hoping he just dropped out of sight and is OK.

 

[JimFuller]

I have about 150 to 200 TDS at 65 PSI. I use the BRS 150 GPD 4 stage and come out with 0 TDS into 70 Gallon RO/DI abd 70 Gallon Saltwater. I am very happy with it.

 

[ReefAddict16]

Comes out at 360 tds. After first three stages it comes out at 4. Then last 2 stages (madcap DI/silicabuster)comes out at 0.
http://spectrapure.com/RO-RODI/RODI...Removal-RO-DI-System-w-SilicaBuster-MaxCap-DI

 

[FDAWG]

In Rancho Cucamonga, I got a TDS of 210 and I’m boosting up my pressure to about 83psi. I’m using a AquaFX Octopus RODI unit 200 GPD and I still have to add the second DI that came with the unit.

 

[coder0000]

I'm scared to check what's coming out of my tap, but I know it's very hard water in my area. I've got the AquaFX Barracuda 4-stage, and it's about 132 TDS after RO (!), and 0 after DI. I just set this up recently, and went through my first DI canister insanely fast. Not surprising if it's 132 TDS going into the resin! I'm thinking of getting the separate 3 stage resin from BRS. Pressure coming in is ~75psi. I was originally going to do the doubler, but it sounds like that would be a bad idea in my situation...

 

[jeffrey holloway]

I run a 6 stage BRS RODI with a booster pump. My TDS out of the Tap is only 4 ppm on average. I guess I should feel lucky, rarely ever have to change the filters. This is the only part of my system I rarely have to pay attention to or fuss with.

 

[samnaz]

My tap TDS is around 80-100.

I add seachem Prime to the tap water, and use it for top off and to mix salt. Easy peasey. I got lucky living in a city with great water quality.

 

[JoshH]

I'm scared to check what's coming out of my tap, but I know it's very hard water in my area. I've got the AquaFX Barracuda 4-stage, and it's about 132 TDS after RO (!), and 0 after DI. I just set this up recently, and went through my first DI canister insanely fast. Not surprising if it's 132 TDS going into the resin! I'm thinking of getting the separate 3 stage resin from BRS. Pressure coming in is ~75psi. I was originally going to do the doubler, but it sounds like that would be a bad idea in my situation...

What kind of membrane is it? My guess is something is amiss if your getting 132 after the membrane, it might not be seated correctly.

 

[JoshH]

I run a 6 stage BRS RODI with a booster pump. My TDS out of the Tap is only 4 ppm on average. I guess I should feel lucky, rarely ever have to change the filters. This is the only part of my system I rarely have to pay attention to or fuss with.

You could probably just run a 3 stage DI with fantastic results as well without sending any waste down the drain.

 

[Dburr1014]

45ish.
My house runs thru a 5ft tall GAC filter, then I have my rodi. Out of my ro filter the tds is 2. The di takes care of the rest.

 

[coder0000]

What kind of membrane is it? My guess is something is amiss if your getting 132 after the membrane, it might not be seated correctly.

Thank you Josh. It turns out it was attributable to the user being a moron and measuring the wrong thing

I reconnected the TDS meter to measure the house line, and it was 130 when I was expecting a much larger value. I then noticed that I had previously been measuring post-carbon/sediment, but BEFORE it was going into the RO membrane (!!). After connecting it all up correctly, it now settles down to 1 TDS after RO. Sheesh! I feel so dumb, but I'm happy that house line isn't as bad as I thought it might be. I still don't have an explanation for why I seem to be going through DI resin pretty quickly, but maybe it's because I am not pre-flushing when I first start. I just replaced the canister right now and will keep an eye on it.

It sounds like I might be a good candidate for the doubler too since I have 70+ psi.

 

[Halal Hotdog]

Thank you Josh. It turns out it was attributable to the user being a moron and measuring the wrong thing

I reconnected the TDS meter to measure the house line, and it was 130 when I was expecting a much larger value. I then noticed that I had previously been measuring post-carbon/sediment, but BEFORE it was going into the RO membrane (!!). After connecting it all up correctly, it now settles down to 1 TDS after RO. Sheesh! I feel so dumb, but I'm happy that house line isn't as bad as I thought it might be. I still don't have an explanation for why I seem to be going through DI resin pretty quickly, but maybe it's because I am not pre-flushing when I first start. I just replaced the canister right now and will keep an eye on it.

It sounds like I might be a good candidate for the doubler too since I have 70+ psi.

I also burn through DI and it is because my source TDS is very high. My pre-filtration removes so much and the DI gets slammed. May want to check what the TDS is after RO before DI to give you a better idea of how well the membranes are doing.