RODI Testing

[Reefugee]

There's been numerous holy wars on RC regarding RODI system. Some people swear that the cheapie Ebay RODI system works great, while others tell you that if you don't spend $200+ on an RODI, you have a piece of junk and your fish will all grow a third eye from the contaminated water.

Anyway - I have a an Ebay (AquaSafe) RODI system rated at 100GPD. According to what I have read, the 100GPD RO membrane has a rejection rate to 90%. The 75GPD unit has a rejection rate of 98%. I have been debating on converting my 100GPD RO to a 75GPD RO.

I also heard that the initial burst of RODI water is usually not that great, so it's bad to run RODI for a short period of time. It is supposed to be better to run the RODI for a less frequent but longer period of time. I decided to do some quick tests.

My RODI unit is about 2 years old. All the pre-filters and the RO membrane are originals. I have replaced only the DI five times in the past two years - usually when the RODI water reads 15+ppm. I just replaced my DI with the Funman1's DI group buy (Thanks Steve!). Below are my TDS reading from my test.

Tap water = 515 ppm (my water seems to vary between 500 to 900ppm)
RO = initially 144 ppm but after a few minutes, it read 6ppm
after DI = 0ppm
water production rate: no where close to 100GPD

So according to my calculation, my RO is removing 98.8% of the TDS. Also - it appears to confirm that running the RODI for frequent short burst is worse than running it for less frequent longer period of time.

Here is the interesting part - my RODI water has read as high as 17ppm before. I can't recall if I tested the water at the "initial burst" or after the water had been running for a while. If it was after the water had been running for a while, I am wondering if the DI could have leached some impurities back into the water.

Anyway - I just though I would share my results with the group.

Now - let the religious war start....

Minh

 

[MrMikeB]

Minh,

That approximates the limited testing I have done on my eBay special. I have a similar setup, except it being only 6 mos old. 0 TDS, and $130 shipped!

 

[funman1]

hahaha
nice work Mihn, thanks for sharing

 

[Buckeye Hydro]

Mihn - To understand better how your system is working, we need the tds readings from 3 locations:

1. Tap water: 515 ppm
2. Water purified by the RO before it reaches the DI stage: ?
3. After the DI: 0 ppm

It is likely that your prefilters are clogged - what this does is reduce the pressure reaching the membrane - which degrades the performance of the membrane. This in turn would lead you to more frequent DI resin changes than would otherwise be the case. Without a pressure gauge you will not be able to tell if the prefilters are clogged - but after two years I think the chances are pretty high that they are.

Remember that your carbon prefilter(s) have a finite capacity to adsorb chlorine. when you exceed that capacity chlorine will reach the membrane and ruin the membrane. Again - this will lead to more frequent DI resin changes than would otherwise be the case.

One of the issues with operation of these systems is the potential for the build up of biological material in the portion of the system exposed to nonchlorinated water. One of the ways to deal with this is changing the prefilters every 6 months. When you do get around to changing your filters you will want to sanitize the system - we recommend you do this once a year.

If your system is one configured with GAC after the DI you are better off removing those post-DI GAC stages.

If your system has a horizontal DI stage you can improve the system performance and cost of operation with the addition of a full size, refillable DI stage.

Russ @ BFS

 

[Reefugee]

Russ,

Thanks for the information. The water purified by the RO before it reaches the DI stage starts out around 144ppm but after running it for a little while, it goes down to 6ppm. I confirmed this twice yesterday. I am wondering if this is normal that it starts out high, but drops down. If it is - then it confirms some some of the recommendation that it is better to run the RODI less frequent for a longer period than more frequently for a shorter period.

I have been a little "lazy" in changing my pre-filters. My new pre-filters should be arriving any day now (ordered them last week). I will also be changing my membrane out pretty soon too. I have been debating whether I should go with the 75 gpd RO membrane (with a new flow restrictor) or 100 gpd RO membrane. I read somewhere that the 75GPD RO membrane gives your a 98% TDS rejection where as the 100 gpd RO membrane give a 90% TDS rejection. But based on my quick test, it appears that my 100 gpd RO membrane is giving be a 98.8% rejection after it's been running for a few minutes.

I have been doing a lot of reading on the pre-filters. Some company recommend a 10 micron sediment filters, and others recommend a 5 micron sediment filters. What are you thoughts? The filter kit I got was a 10 micron sediment, 5 micron coconut carbon 5 micron, and then 1 micron coconut carbon filter from AirWaterIce.

I also have SpectraPure 4 stage 75gpd RODI system (picked it up used for $20). I don't know how old the filters are but the unit has been siting in my garage for at least a year now. Last week, I used it to make water. With new DI resin, the water quality was 0 ppm. I didn't measure the RO water. I am considering purchasing another 10" canister, and making it a 5 stage RODI system. This system (without the DI) would normally feed my fridge's water and icemaker. Then in an emergency, I can always use this system for making water.

The only thing I really don't like about the AquaSafe system is that the canister is not clear like the SpectraPure system. But for a sub $100 unit with a water storage tank (used for the ice maker) - I can't really complain.

Minh

<a href=showthread.php?s=&postid=9680856#post9680856 target=_blank>Originally posted</a> by BuckeyeFS
Mihn - To understand better how your system is working, we need the tds readings from 3 locations:

1. Tap water: 515 ppm
2. Water purified by the RO before it reaches the DI stage: ?
3. After the DI: 0 ppm

It is likely that your prefilters are clogged - what this does is reduce the pressure reaching the membrane - which degrades the performance of the membrane. This in turn would lead you to more frequent DI resin changes than would otherwise be the case. Without a pressure gauge you will not be able to tell if the prefilters are clogged - but after two years I think the chances are pretty high that they are.

Remember that your carbon prefilter(s) have a finite capacity to adsorb chlorine. when you exceed that capacity chlorine will reach the membrane and ruin the membrane. Again - this will lead to more frequent DI resin changes than would otherwise be the case.

One of the issues with operation of these systems is the potential for the build up of biological material in the portion of the system exposed to nonchlorinated water. One of the ways to deal with this is changing the prefilters every 6 months. When you do get around to changing your filters you will want to sanitize the system - we recommend you do this once a year.

If your system is one configured with GAC after the DI you are better off removing those post-DI GAC stages.

If your system has a horizontal DI stage you can improve the system performance and cost of operation with the addition of a full size, refillable DI stage.

Russ @ BFS

 

[jlfnjlf]

Tagging along...

I want to replace my prefilters, so I think this could be very helpful to me.

John

 

[Buckeye Hydro]

<a href=showthread.php?s=&postid=9681544#post9681544 target=_blank>Originally posted</a> by Reefugee
Russ,

Thanks for the information. The water purified by the RO before it reaches the DI stage starts out around 144ppm but after running it for a little while, it goes down to 6ppm. I confirmed this twice yesterday. I am wondering if this is normal that it starts out high, but drops down. If it is - then it confirms some some of the recommendation that it is better to run the RODI less frequent for a longer period than more frequently for a shorter period.

I have been a little "lazy" in changing my pre-filters. My new pre-filters should be arriving any day now (ordered them last week). I will also be changing my membrane out pretty soon too. I have been debating whether I should go with the 75 gpd RO membrane (with a new flow restrictor) or 100 gpd RO membrane. I read somewhere that the 75GPD RO membrane gives your a 98% TDS rejection where as the 100 gpd RO membrane give a 90% TDS rejection. But based on my quick test, it appears that my 100 gpd RO membrane is giving be a 98.8% rejection after it's been running for a few minutes.

I have been doing a lot of reading on the pre-filters. Some company recommend a 10 micron sediment filters, and others recommend a 5 micron sediment filters. What are you thoughts? The filter kit I got was a 10 micron sediment, 5 micron coconut carbon 5 micron, and then 1 micron coconut carbon filter from AirWaterIce.

I also have SpectraPure 4 stage 75gpd RODI system (picked it up used for $20). I don't know how old the filters are but the unit has been siting in my garage for at least a year now. Last week, I used it to make water. With new DI resin, the water quality was 0 ppm. I didn't measure the RO water. I am considering purchasing another 10" canister, and making it a 5 stage RODI system. This system (without the DI) would normally feed my fridge's water and icemaker. Then in an emergency, I can always use this system for making water.

The only thing I really don't like about the AquaSafe system is that the canister is not clear like the SpectraPure system. But for a sub $100 unit with a water storage tank (used for the ice maker) - I can't really complain.

Minh

Yes - the phenonenom is called TDS CREEP, and is common to all RO systems.

Yes - you'll find that the 100 gpd filtec membrane rejects 90% of the feed water tds. The 75 gpd membrane rejects 96 to 98%.

If you have good pressure, and if you do not have a problem with heavy sediment loads, a 1 micron sediment filter is good. Follow that with a carbon block of a similar micron rating. You don't want your carbon block acting as a sediment filter.

 

[Buckeye Hydro]

<a href=showthread.php?s=&postid=9681544#post9681544 target=_blank>Originally posted</a> by Reefugee
Russ,

Thanks for the information. The water purified by the RO before it reaches the DI stage starts out around 144ppm but after running it for a little while, it goes down to 6ppm. I confirmed this twice yesterday. I am wondering if this is normal that it starts out high, but drops down. If it is - then it confirms some some of the recommendation that it is better to run the RODI less frequent for a longer period than more frequently for a shorter period.

I have been a little "lazy" in changing my pre-filters. My new pre-filters should be arriving any day now (ordered them last week). I will also be changing my membrane out pretty soon too. I have been debating whether I should go with the 75 gpd RO membrane (with a new flow restrictor) or 100 gpd RO membrane. I read somewhere that the 75GPD RO membrane gives your a 98% TDS rejection where as the 100 gpd RO membrane give a 90% TDS rejection. But based on my quick test, it appears that my 100 gpd RO membrane is giving be a 98.8% rejection after it's been running for a few minutes.

I have been doing a lot of reading on the pre-filters. Some company recommend a 10 micron sediment filters, and others recommend a 5 micron sediment filters. What are you thoughts? The filter kit I got was a 10 micron sediment, 5 micron coconut carbon 5 micron, and then 1 micron coconut carbon filter from AirWaterIce.

I also have SpectraPure 4 stage 75gpd RODI system (picked it up used for $20). I don't know how old the filters are but the unit has been siting in my garage for at least a year now. Last week, I used it to make water. With new DI resin, the water quality was 0 ppm. I didn't measure the RO water. I am considering purchasing another 10" canister, and making it a 5 stage RODI system. This system (without the DI) would normally feed my fridge's water and icemaker. Then in an emergency, I can always use this system for making water.

The only thing I really don't like about the AquaSafe system is that the canister is not clear like the SpectraPure system. But for a sub $100 unit with a water storage tank (used for the ice maker) - I can't really complain.

Minh

Yes - the phenomenon is called TDS CREEP, and is common to all RO systems.

Yes - you'll find that the 100 gpd Filmtec membrane rejects 90% of the feed water tds. The 75 gpd membrane rejects 96 to 98%.

If you have good pressure, and if you do not have a problem with heavy sediment loads, a 1 micron sediment filter is good. Follow that with a carbon block of a similar micron rating. You don't want your carbon block acting as a sediment filter.

 

[Reefugee]

When I arrived home, my new pre-filters and inline TDS meter were sitting on my porch. I purchased the filter from AirWaterIce (great customer service). The filters were a 10 micron sediment fiter, a 5 micron Carbon filter, and a 1 micron carbon fitler. All the prefilters were replaced.

Picture of the old sediment filter vs the new one. I guess I should have changed out the filter a LONG time ago.

My tap water TDS read 546ppm. This is from the same faucet that feeds my RODI system:

This is the water after it has gone through the RODI system. The initial water quality was 50ppm, but after about 10 minutes, it was down to 2ppm. Basically the prefilter and the RO removed 99.6% of my TDS.

This is the water after it's been through both the RO and the DI. The DI was just replaced last week. TDS = 0

Now that I was done with my little test, I turned off my RODI system. About 10 minutes later, my water post-RO but pre-DI crept up to 10ppm.

So out of curiosity, I turn on my RODI system and let it run for about 10 minutes. The post-RO water read 2ppm again.

Here's a picture of my AquaSafe RODI system. I modified the DI canister so that it stands upright. The water from the RO flows through the bottom of DI canister and then exits through the top. The reason why I did this is so that the water must past through DI to exit the canister. In the horizontal position, it was possible for some water to barely have any contact with the DI resin.

Not bad for a system that I purchased for $96 (shipped) two years ago.

Minh

 

[CaptiveReefSystems]

there in lye's the problem with the less expensive filter systems. Having the ability to visually inspect the filters using clear canisters is a big help. I would be willing to bet that Minh would have changed his filter cartridge much sooner if he could have seen it.

Also, to help decrease the waste water production of the RO, I always install a boost pump.

 

[Reefugee]

Bruce - I agree with you that had I seen my filter, I would have changed it much soon. I am thinking of changing out the sediment filter with a clear housing unit. It should a quick and simple process. I just need to make sure that I change the filter every 9 months to a year. No more going 2 years on the pre-filters before changing it out.

 

[Jacob D]

Hey Minh. Was good seeing you today.

Good thread. I have the Aquasafe 75 GPD unit, but running a 100 GPD RO membrane (it fit, so what the hey). I change everything out yearly and it has kept my TDS at zero. I have been using Aquasafe RO membranes, and DI cartridges. Until recently I had been using the prefilters that came with my setup originally. I tried some Home Depot cheapo models and they burned up fast - I would not recommend using those.

I'm planning to order some SpectraPure prefilters to see if there's a difference. I might try to get ahold of their RO membrane too, not sure if it will fit though. And, unlike your setup, mine is older (going on 4 years) so the DI is not re-fillable.

I'm kind of debating just buying a whole new setup, I paid $69 + shipping for mine and it came with TDS meter and enough replacements to last me until recently... I think I got my money's worth

 

[Reefugee]

In another thread, someone pointed out that my readings might be wrong. I decided to redo the same test, but to verify the result of the inline TDS meter with my handheld TDS meter. Here's what I posted:

-----------------------------
Rob,

As promised, I just re-did the RO water reading. According to the inline TDS meter, the water was 3ppm. I went ahead tested the same water with a handheld water meter, and it measured 6ppm. Ironically, when I put the inline TDS meter's probe into the water container, it reads 6ppm. I confirmed this measurement twice. The two containers were the "sterile" medical containers.

Here is my newest reading:
Tap water: 545 ppm
RO water: 6 ppm (see above)
DI water: 0 ppm verified with inline TDS meter and handheld meter

RO membrane efficiency: 98.9% rejection rate


Minh

 

[Cbrewer]

I am tired of having to run to Pure water every week and lug around 5g bottles of water. However, i am what you might called handi-incapable when it comes to projects. How difficult was this to install?