How far to chase RO water for a high-end SPS tank.

Randy Holmes-Farley · Jan 10, 2023

What is the tds pre di?

Unless it is 2-4 ppm tds, collecting until the tds reads 2 ppm in the effluent us not going to cut down on di costs much.

There is also a substantial concern that di effluent when the tds first rises may be worse than no di, because weekly bound ions will be displaced by tighter bound ions, potentially releasing substantial ammonia and silicate.

vetteguy53081 · Jan 10, 2023

Reefer1978 said:
How important is 0 tds? New Jersey water is pretty hard, close to 500 coming into the house, tds coming out of DI is 2, but burning through DI media. Is investment into a high end RODI worth it? Currently takes 2 full DI cannisters to make 55g.

For some details:

5 stage RO, all brand new filters

2 stage DI

Checked pre-DI Co2, and it doesn't seem too bad, 7.8 Ph coming out of RO, 7.96 Ph after de-gassing outdoors, so I suspect that's not what's eating through the resin.

I lived in Passaic county, NJ and they had during winter levela of:
High chlorine
mercury
lead
uranium

Reefer1978 · Jan 10, 2023

Tamberav said:
perhaps a dual membrane then?

and the pressure is okay?

Yep, pressure is ok. Also on the list of considerations.

MarsReefer said:
Putting 60 tds through resin is going to burn through quickly.

I have 400 TDS water and I get 3-5 tds after the membrane. You’ll never reduce resin consumption with such high tds after the membrane.

I’d look at getting a second carbon block, BRS has some videos on setting up carbon like that. I’d also check that your membrane is still good, 88% is really low for a membrane.

Will take a look.

vetteguy53081 said:
I lived in Passaic county, NJ and they had during winter levela of:
High chlorine
mercury
lead
uranium

Wonderful LOL... more to research.

Reefer1978 · Jan 10, 2023

Randy Holmes-Farley said:
What is the tds pre di?

Unless it is 2-4 ppm tds, collecting until the tds reads 2 ppm in the effluent us not going to cut down on di costs much.

There is also a substantial concern that di effluent when the tds first rises may be worse than no di, because weekly bound ions will be displaced by tighter bound ions, potentially releasing substantial ammonia and silicate.

Pre-DI TDS is in the 55-60 range. I have to say might blown with the last sentence. Is the solution to first flush pre-di? i.e. few gallons?

Randy Holmes-Farley · Jan 10, 2023

Reefer1978 said:
Pre-DI TDS is in the 55-60 range. I have to say might blown with the last sentence. Is the solution to first flush pre-di? i.e. few gallons?

55 ppm tds will necessarily deplete a di fast.
If you do not alter that with a different ro membrane, then I suggest using 2 di in series. When the tds in between the two rises to, say, 10 ppm tds, toss the first one, move the second one into the first position, and put a new one in position 2. That’s a great way to maximize di usage without letting the effluent tds rise.

Reefer1978 · Jan 10, 2023

Randy Holmes-Farley said:
55 ppm tds will necessarily deplete a di fast.
If you do not alter that with a different ro membrane, then I suggest using 2 di in series. When the tds in between the two rises to, say, 10 ppm tds, toss the first one, move the second one into the first position, and put a new one in position 2. That’s a great way to maximize di usage without letting the effluent tds rise.

Thanks @Randy Holmes-Farley , that's exactly how I have it. After 55g, first canister is gone, second is half way gone. What I do at this point is move second to first, and then put a fresh one into second.

Potatohead · Jan 10, 2023

I don't see this talked about much in RODI threads but pressure is extremely important.

I haven't seen posted what your current pressure into the membrane is. I am going to guess 40-50 psi. If you can get this up to more like 80-90 and halve your TDS coming out of the membrane (and it will probably help more than that) you will double the life of your DI. This will pay for the booster pump very quickly.

60 TDS out of the membrane is way, way too much. There is no reason you can't get that into the teens at worst.

Malcontent · Jan 10, 2023

vetteguy53081 said:
I lived in Passaic county, NJ and they had during winter levela of:
High chlorine
mercury
lead
uranium

I'm curious how high the chlorine was.

Reefer1978 · Jan 10, 2023

Potatohead said:
I don't see this talked about much in RODI threads but pressure is extremely important.

I haven't seen posted what your current pressure into the membrane is. I am going to guess 40-50 psi. If you can get this up to more like 80-90 and halve your TDS coming out of the membrane (and it will probably help more than that) you will double the life of your DI. This will pay for the booster pump very quickly.

60 TDS out of the membrane is way, way too much. There is no reason you can't get that into the teens at worst.

I did post it I believe, but it's easily missed. I am at 75 PSI.

spsick · Jan 10, 2023

OP, it may help readers of you add all the additional I go you’ve trickled in to the original post.

As others have noted, your TDS coming out of the membrane is way higher than it should be. What gpd membrane do you have and what flow restrictor do you have so we can make sure your reject ratio is correct.

Switchtong to 3 stage cation, anion, mixed bed did cut my DI usage immensely but nothing is going to help with 60tds coming out of your membrane.

thedon986 · Jan 10, 2023

Reefer1978 said:
I did post it I believe, but it's easily missed. I am at 75 PSI.

My booster gets me up to 100-110psi. Maybe a high pressure pump would help, too?

Reefer1978 · Jan 10, 2023

spsick said:
OP, it may help readers of you add all the additional I go you’ve trickled in to the original post.

As others have noted, your TDS coming out of the membrane is way higher than it should be. What gpd membrane do you have and what flow restrictor do you have so we can make sure your reject ratio is correct.

Switchtong to 3 stage cation, anion, mixed bed did cut my DI usage immensely but nothing is going to help with 60tds coming out of your membrane.

Original post updated, thanks.

thedon986 said:
My booster gets me up to 100-110psi. Maybe a high pressure pump would help, too?

Unfortunately it's not adjustable.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~
I think I am getting to the bottom of the issue, and simply stated the RO is not designed for how I want to use it. I spoke to the vendor (iSpring) and their rating is 80-90% rejection. Looks like I am pretty much within the spec going 500 (ish) >>>> 60. I am already researching a replacement unit for the tank, and will keep this one for our drinking water only.

spsick · Jan 10, 2023

Reefer1978 said:
Original post updated, thanks.

Unfortunately it's not adjustable.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~
I think I am getting to the bottom of the issue, and simply stated the RO is not designed for how I want to use it. I spoke to the vendor (iSpring) and their rating is 80-90% rejection. Looks like I am pretty much within the spec going 500 (ish) >>>> 60. I am already researching a replacement unit for the tank, and will keep this one for our drinking water only.

Your 70psi is absolutely fine. I’m not sure what the unit looks like but you can usually put different membranes in most. Filmtec 75gpd membranes are like 99% rejection. You would just maybe need to change the flow restrictor if it’s a different gpd. I honestly didn’t even know they made membranes with only 80% rejection.

chipmunkofdoom2 · Jan 10, 2023

A lot of people can play fast and loose with their RO systems. They get away with it because their water is pretty soft. You're not one of those people. You're going to need to run your system as optimally as possible to get the best results.

The biggest thing nobody has mentioned is check your recovery rate. Recovery is how much brine (waste water) vs permeate (freshwater) is produced. Many RO unit manufacturers put comically small flow restrictors on their systems. This "saves" water by forcing more water through the membrane, but this only works if your water is relatively clean. If you have high TDS, you're killing your membrane. Without enough brine flowing over the membrane, it's prone to fouling. TDS is also likely worse.

You want to shoot for at least 1:4 permeate to brine. That is, for every cup of fresh water that your unit produces, it should produce 4 cups of waste water. That might sound like a lot, but RO membranes are designed to recover only a small amount of the input. Dow tests their membranes with 15% recovery, but they get 99% rejection rates; in other words, the membrane removes 99% of the TDS. To put that into context, your post membrane TDS would be 5 ppm if you got 99% rejection.

Other than that, just practice good RO system hygiene. Use a very small sediment filter (1 micron or less). Sediment filters are cheap and protect everything downstream, so it's worth it to stay on top of them. Replace the sediment filter if the pressure drops over the prefilters (requires a pressure gauge before and after the prefilters). Make sure your carbon blocks are still good by testing the brine for chlorine occasionally. Replace the carbon blocks when you detect any chlorine. Make sure your membrane is getting at least 50 PSI. If you want to do more pressure, that's fine, but it's not really necessary. Dow tests at 50 PSI and gets 99% rejection rates. Consider upgrading to separate cation/anion stages.

As a closing thought, if you're testing at least 50 PSI right before your membrane and you're getting over 50 ppm, your membrane is shot. That's only a 90% rejection rate (50 ppm / 500 ppm at the tap). A good 75GPD membrane will give you 96% or better.

EDIT: another closing thought: consider getting a water softener, if not for your whole house, then at least for your RO system. Water softeners work by exchanging the TDS in your water for regular sodium chloride. Regular salt is much easier for your membrane to remove than calcium, magnesium, and other minerals in high-TDS tap water.

bee144 · Jan 10, 2023

I’m confused here. You’ve spent thousands if not 10s of thousands on what you describe as a high end sps tank. And you’re going the cheap route with a simple 5 stage system?

not to mention all the time to troubleshoot.

7 Stage PRO Plus 75 GPD RO/DI System - Bulk Reef Supply

Make up to 75 Gallons per day of the Best RODI Water your Reef Tank Will Ever Get! Super efficient with DI consumption Includes BRS Pro resin Produce 0 TDS water Minimal wastewater Includes Float Valve and Inline Ball Valve Multiple source water connections Mur-lok Push Connect dual EPDM O-Ring...

www.bulkreefsupply.com

You really should just upgrade to a 7 stage and then see where you are at. 500 tds water is really bad so you need to bring in the big guns. See how it performs and then come back to us.

and yes, you need to flush your membrane for 10 minutes before and after producing water.

Reefer1978 · Jan 10, 2023

chipmunkofdoom2 said:
A lot of people can play fast and loose with their RO systems. They get away with it because their water is pretty soft. You're not one of those people. You're going to need to run your system as optimally as possible to get the best results.

The biggest thing nobody has mentioned is check your recovery rate. Recovery is how much brine (waste water) vs permeate (freshwater) is produced. Many RO unit manufacturers put comically small flow restrictors on their systems. This "saves" water by forcing more water through the membrane, but this only works if your water is relatively clean. If you have high TDS, you're killing your membrane. Without enough brine flowing over the membrane, it's prone to fouling. TDS is also likely worse.

You want to shoot for at least 1:4 permeate to brine. That is, for every cup of fresh water that your unit produces, it should produce 4 cups of waste water. That might sound like a lot, but RO membranes are designed to recover only a small amount of the input. Dow tests their membranes with 15% recovery, but they get 99% rejection rates; in other words, the membrane removes 99% of the TDS. To put that into context, your post membrane TDS would be 5 ppm if you got 99% rejection.

Other than that, just practice good RO system hygiene. Use a very small sediment filter (1 micron or less). Sediment filters are cheap and protect everything downstream, so it's worth it to stay on top of them. Replace the sediment filter if the pressure drops over the prefilters (requires a pressure gauge before and after the prefilters). Make sure your carbon blocks are still good by testing the brine for chlorine occasionally. Replace the carbon blocks when you detect any chlorine. Make sure your membrane is getting at least 50 PSI. If you want to do more pressure, that's fine, but it's not really necessary. Dow tests at 50 PSI and gets 99% rejection rates. Consider upgrading to separate cation/anion stages.

As a closing thought, if you're testing at least 50 PSI right before your membrane and you're getting over 50 ppm, your membrane is shot. That's only a 90% rejection rate (50 ppm / 500 ppm at the tap). A good 75GPD membrane will give you 96% or better.

EDIT: another closing thought: consider getting a water softener, if not for your whole house, then at least for your RO system. Water softeners work by exchanging the TDS in your water for regular sodium chloride. Regular salt is much easier for your membrane to remove than calcium, magnesium, and other minerals in high-TDS tap water.

Thanks, I am going to mess around with recovery rate and you are correct, I haven't measured that. Spec is listing 1.5:1, which looks like is not ideal. Membrane cannot be shot, as it's brand new. But, is there such a thing as a crappy Membraine?

bee144 said:
I’m confused here. You’ve spent thousands if not 10s of thousands on what you describe as a high end sps tank. And you’re going the cheap route with a simple 5 stage system?

not to mention all the time to troubleshoot.

7 Stage PRO Plus 75 GPD RO/DI System - Bulk Reef Supply

Make up to 75 Gallons per day of the Best RODI Water your Reef Tank Will Ever Get! Super efficient with DI consumption Includes BRS Pro resin Produce 0 TDS water Minimal wastewater Includes Float Valve and Inline Ball Valve Multiple source water connections Mur-lok Push Connect dual EPDM O-Ring...

www.bulkreefsupply.com

You really should just upgrade to a 7 stage and then see where you are at. 500 tds water is really bad so you need to bring in the big guns. See how it performs and then come back to us.

and yes, you need to flush your membrane for 10 minutes before and after producing water.

Your potential confusion is due to jumping to conclusions. Let me explain why:
1. The "build" is in progress, so I am doing as much as possible analysis / design ahead of time. No SPS yet, no "You’ve spent thousands if not 10s of thousands on what you describe as a high end sps tank."
2. I am trying to re-use an existing RODI I already have, if it doesn't work, I will get a new one
3. I am already at 7 stages, but I can always add more if I decide to go there.
4. RO is on auto-flush, and I did manually flush before this test.

Malcontent · Jan 10, 2023

Reefer1978 said:
2. I am trying to re-use an existing RODI I already have, if it doesn't work, I will get a new one

You should be able to just replace the membranes with high quality, high rejection rate ones.

chipmunkofdoom2 · Jan 10, 2023

Reefer1978 said:
Thanks, I am going to mess around with recovery rate and you are correct, I haven't measured that. Spec is listing 1.5:1, which looks like is not ideal. Membrane cannot be shot, as it's brand new. But, is there such a thing as a crappy Membraine?

Some are better than others in terms of rejection rates. The 75 GPD is a popular one because the rejection rate is so high. What brand and GPD is the membrane?

Reefer1978 · Jan 10, 2023

Malcontent said:
You should be able to just replace the membranes with high quality, high rejection rate ones.

chipmunkofdoom2 said:
Some are better than others in terms of rejection rates. The 75 GPD is a popular one because the rejection rate is so high. What brand and GPD is the membrane?

The system is from iSpring, it's their 500GPD unit. The membrane is 500GPD, 3" by 12", so not too many options.