Stupid question about RO/DI water

[stanleo]

Should you let the water that comes out of the unit drain for a while before you keep it? I have been running my unit for about 45 min and always use all the water when it first comes out. I used the meter that came with the unit and in the bucket it reads 40ppm. I tested the water as its coming out in a separate glass and its reading 3ppm. Have I been using bad water all this time?

 

[homefry319]

is the bucket clean?

 

[stanleo]

its the same bucket I use for salt water storage. Should I rinse it out before I refill it even if I only use that bucket for saltwater?

 

[Mike J.]

RO/DI water should be 0 TDS after going through the DI. Mine is 2 - 4 ppm out of RO filter and 0 out of DI.

 

[homefry319]

its the same bucket I use for salt water storage. Should I rinse it out before I refill it even if I only use that bucket for saltwater?

theres no need to rinse it out, but you maybe picking up some readings from the lingering salts in the bucket

 

[GrizFyrFyter]

theres no need to rinse it out, but you maybe picking up some readings from the lingering salts in the bucket

+1

Dissolved salt will raise tds readings. Using the bucket is fine if it is salt that is causing the increase. Keep testing in a clean container to monitor your di effectiveness.

 

[KoleTang]

its the same bucket I use for salt water storage. Should I rinse it out before I refill it even if I only use that bucket for saltwater?

Use a clean container for testing. Even if it is just salt and minerals that are safe for the tank they still count as TDS and could mess with your test.

 

[ReefKeeper09]

I actually have to run mine for about 2-3 mins at first start up each time(After its sat for some time). It reads a 2-3ppm before dropping to 0 after about 2-3 Minutes of running. Other than that it reads 0ppm @ all times!

 

[KoleTang]

I actually have to run mine for about 2-3 mins at first start up each time(After its sat for some time). It reads a 2-3ppm before dropping to 0 after about 2-3 Minutes of running. Other than that it reads 0ppm @ all times!

I noticed that on mine as well. It was all the way up at 14 so I let it run for a few minutes as well as turned on the flush kit and it dropped down to 1 (which is 0 since the meter has an accuracy of +/- 1)

 

[ReefKeeper09]

Yeah, the highest I have seen mine so far on a fresh start was 5ppm. I haven't seen it much higher. Though, these are still newer cartridges.

 

[AZDesertRat]

I answered a similar question just this morning here:
RO DI Help - The Reef Tank

All membranes suffer from TDS creep meaning when sitting idle the tap water TDS osmoses from the tap side to the treated side since the treated water is agressive and trying to get back to its normal "dirty" state. If possible install a DI bypass valve (a simple 1/4" tee and ball valve) so you can open it up and flush the TDS creep out before letting it hit your DI resin and shorten its life. If not always let at least a few ounces go down the drain before capturing your treated water, a handheld TDS meter will tell you when it is 0 or at its lowest point.

 

[Mike J.]

I answered a similar question just this morning here:
RO DI Help - The Reef Tank

All membranes suffer from TDS creep meaning when sitting idle the tap water TDS osmoses from the tap side to the treated side since the treated water is agressive and trying to get back to its normal "dirty" state. If possible install a DI bypass valve (a simple 1/4" tee and ball valve) so you can open it up and flush the TDS creep out before letting it hit your DI resin and shorten its life. If not always let at least a few ounces go down the drain before capturing your treated water, a handheld TDS meter will tell you when it is 0 or at its lowest point.

AZDesertRat always has the best answers. I've been doing this a long time and I am going to put a T with a shut off to do this. Anything to help my DI resin last longer.

Thanks for the tip.

 

[blufin]

RO/DI water should be 0 TDS after going through the DI. Mine is 2 - 4 ppm out of RO filter and 0 out of DI.

What is the highest TDS reading that you guys would consider using? My RO/DI water reads 10-20 ppm. I felt pretty good getting these numbers, but I'm starting to think it should be much lower to get my persistent GHA problem under control. My tap water reads 610 before my system. I recently changed the di resin and within 10 gallons, the reading had jumped to 9ppm. Is there anything else associated with an ro/di system that would cause the tds to increase so quickly?

 

[AZDesertRat]

0-1.
Since you have no idea what the TDS is made up of 0 is your goal.

If you are seeing a reading that quickly Isuspect your RO membrane is not as efficient as it shoud be. My tap TDS is in the 550-850 range and I always get 0 TDS for hundreds of gallons or more. My RO only TDS varies between 2 and 3.

What is your tap water TDS, RO only TDS before the DI and final RO/DI TDS taken directly from the unit not from a storage vessel or bucket? What is your water temperature and water pressure? What is your exact measured waste ratio? How old is your RO membrane and what brand and GPD is it?

 

[blufin]

0-1.
Since you have no idea what the TDS is made up of 0 is your goal.

If you are seeing a reading that quickly Isuspect your RO membrane is not as efficient as it shoud be. My tap TDS is in the 550-850 range and I always get 0 TDS for hundreds of gallons or more. My RO only TDS varies between 2 and 3.

What is your tap water TDS, RO only TDS before the DI and final RO/DI TDS taken directly from the unit not from a storage vessel or bucket? What is your water temperature and water pressure? What is your exact measured waste ratio? How old is your RO membrane and what brand and GPD is it?

I will find the answers to these questions and get back to you. I'm on a well system so I always thought it was par for the course. Hopefully I can get this corrected and get better water/life out of my system. Currently fighting GHA that won't go away. Cut down lighting, feeding and now focusing on RO.

 

[AZDesertRat]

Any RO/DI should be capable of 0 TDS, the difference is how long it stays there.
Some less expensive systems may not give you much 0 TDS, others may give you 1000 gallons or more. My tap TDS averages 550 or so and I have Co2 in my source water and I get over 1000 gallons per DI cartridge.

 

[blufin]

Any RO/DI should be capable of 0 TDS, the difference is how long it stays there.
Some less expensive systems may not give you much 0 TDS, others may give you 1000 gallons or more. My tap TDS averages 550 or so and I have Co2 in my source water and I get over 1000 gallons per DI cartridge.

Okay, here's the scoop. The membrane has less than 100 gallons through it, although it is over a year or 2 old. I fired up the system a while back and saw how fast the DI cartridge was exhausted and shut it off. The system sat for a few years unused. The sediment, both carbons, post filter(smell/taste) and membrane are a few years old, with only about 100 gallons through them. I recently turned it back on and changed the DI resin. New resin gives me 0 TDS for the first 5-7 gallons. After that, it gradually climbs to 10ppm after 30 gallons. DI resin changes colors within 30 gallons. The system is 100gpd and I'm not sure of the brand. The LFS sells it, so that's what I got. Incoming water to RO/DI system about 79F.
The waste/collected ratio is less than 4:1. I collected 250ml waste water to about 40ml filtered water.
I am on a well system, and the water pressure at the water softener outside is 55psi max. My TDS tap water is 644, post membrane is 309, post taste/smell cartridge is 83 and ultimate TDS is 0 for the 1st few gallons and climbs as noted above. I included a few photos for reference.

Whatcha think?

I suspect the membrane should be changed, but with only about 100g through it, I thought it would fly. Even when new in the past, the DI resin would be exhausted just as quickly.

 

[AZDesertRat]

The RO membrane is shot for sure, with a tap TDS of 644 you should be seeing a RO only TDS of no more than 65 with the Dow Filmtec 100 GPD or around 25 if it is the GE Water 100 GPD which I doubt.

The 100 GPD Dow Filmtec is the absolute worst choice of membranes there is for a RO/DI since it is not actually a Reverse Osmosis membrane but only a Nano Filter membrane thus 90% rejection rate when new versus 96-98% rejection rate for the GE Water or the Dow Filmtec 75 GPD, both of which are real RO membranes.

Once they have had water through them they must say wet at all times or they are done for.

Another thing is unless you are using the system for drinking water only, take the post GAC filter and throw it as far as you possibly can, it actually adds TDS to the water and should only be used for RO only drinking water taste and odor. They have absolutely no place in a RO/DI system.

The small hollow horizontal tubes do not make good DI filters either, they have horrible flow characteristics and allow the water to take the path of least resistance by channeling or short circuiting along the bottom so not all resin and water come into contact with each other.

Fixing your present system would involve a new 75 GPD Dow Filmtec or better yet treated and tested Spectrapure 90 GPD high rejection rate RO membrane or even better still their 99% guaranteed rejection rate membrane and a matched flow restrictor you can adjust to an exact 4:1 waste ratio yourself based on your unique water conditions, a new 1 micron or 0.5 micron sediment filter, a new 1 or 0.5 micron carbon block and a new DI cartridge which would fit in the extra vertical canister that now holds the unneeded second carbon block. Another thing you will need is an inline pressure gauge so you can monitor headloss through the sediment and carbon block filters.

When you add it all up you will be spending as much or more for all of that as you would on a new system with all of that included. Depending on the membrane and quality you will spend $30 to $50 on the membrane and another $5-$8 on a flow restrictor. A 0.5 micron sediment filter, 0.5 carbon block and refillable DI filter will run you about $45-$50 and the 1 micron sediment and carbon with a refillable DI is around $35-$40. An inline pressure gauge kit is around $15 and if you do use the system for drinking water also the post GAC filter is about $15 and a check valve to seperate the RO drinking water from the RO/DI aquarium water is another $9 or $10. Add all this up and you have between $90 and $180 or so to bring it up to working condition.

For comparison take a look at the Spectrapure MPDI for $189 with the 1 micron filters or even better the CSPDI with 0.5 micron filters and a dual inline TDS meter on sale for the same $189 or Buckeye Hydro has their 75 GPD Premium for $150-$160 with a 1 micron sediment and 0.5 micron carbon with either a non tested or tested membrane. Or PurelyH2o has their Optima series in the same price range.

 

[blufin]

The RO membrane is shot for sure, with a tap TDS of 644 you should be seeing a RO only TDS of no more than 65 with the Dow Filmtec 100 GPD or around 25 if it is the GE Water 100 GPD which I doubt.

The 100 GPD Dow Filmtec is the absolute worst choice of membranes there is for a RO/DI since it is not actually a Reverse Osmosis membrane but only a Nano Filter membrane thus 90% rejection rate when new versus 96-98% rejection rate for the GE Water or the Dow Filmtec 75 GPD, both of which are real RO membranes.

Once they have had water through them they must say wet at all times or they are done for.

Another thing is unless you are using the system for drinking water only, take the post GAC filter and throw it as far as you possibly can, it actually adds TDS to the water and should only be used for RO only drinking water taste and odor. They have absolutely no place in a RO/DI system.

The small hollow horizontal tubes do not make good DI filters either, they have horrible flow characteristics and allow the water to take the path of least resistance by channeling or short circuiting along the bottom so not all resin and water come into contact with each other.

Fixing your present system would involve a new 75 GPD Dow Filmtec or better yet treated and tested Spectrapure 90 GPD high rejection rate RO membrane or even better still their 99% guaranteed rejection rate membrane and a matched flow restrictor you can adjust to an exact 4:1 waste ratio yourself based on your unique water conditions, a new 1 micron or 0.5 micron sediment filter, a new 1 or 0.5 micron carbon block and a new DI cartridge which would fit in the extra vertical canister that now holds the unneeded second carbon block. Another thing you will need is an inline pressure gauge so you can monitor headloss through the sediment and carbon block filters.

When you add it all up you will be spending as much or more for all of that as you would on a new system with all of that included. Depending on the membrane and quality you will spend $30 to $50 on the membrane and another $5-$8 on a flow restrictor. A 0.5 micron sediment filter, 0.5 carbon block and refillable DI filter will run you about $45-$50 and the 1 micron sediment and carbon with a refillable DI is around $35-$40. An inline pressure gauge kit is around $15 and if you do use the system for drinking water also the post GAC filter is about $15 and a check valve to seperate the RO drinking water from the RO/DI aquarium water is another $9 or $10. Add all this up and you have between $90 and $180 or so to bring it up to working condition.

For comparison take a look at the Spectrapure MPDI for $189 with the 1 micron filters or even better the CSPDI with 0.5 micron filters and a dual inline TDS meter on sale for the same $189 or Buckeye Hydro has their 75 GPD Premium for $150-$160 with a 1 micron sediment and 0.5 micron carbon with either a non tested or tested membrane. Or PurelyH2o has their Optima series in the same price range.

Thanks for the info Rat. Even though the membrane did stay wet while it was not being used, it looks like it was the wrong one to begin with. That explains why the DI resin was getting exhausted so quickly. It seems my system was more intended for a drinking system than it was for getting pure RO/DI for an aquarium. I'll probably just scrap the current setup instead of retrofitting what I have. It would be nice to have the inline TDS.