Basic RODI question

[Jay Hemdal]

I have a rather basic RODI question. I have a RO Buddie 50gpd RODI system for my home aquarium. The membrane and sediment cartridges are working well, production rate hasn't dropped). However, the DI cart has completely changed color and is exhausted. My raw feed runs about 400 ppm dissolved solids (I have a water softener on a well). When the DI was fresh, I was getting 0 to 1 ppm TDS in the product water. Now I'm getting 3.

My question is: how critical is this 2 ppm increase? Is that 2 ppm just a percentage of the total mix of TDS (1/2% increase, mostly softener salt) or is that 2% comprised preferentially of more problematic compounds such as heavy metals or organic toxins?

Thanks,

Jay

 

[Jekyl]

@Randy Holmes-Farley @vetteguy53081

 

[WVNed]

Using roundish numbers ~ 95% of everything in the water should have been removed before the DI stage.

Copied from Reefkeeping mag

Ions such as sodium (Na+), copper (Cu++ or Cu+), ammonium (NH4+), phosphate (PO4---), silicate (Si(OH)3O-), and acetate (CH3CO2-) all get caught. by the DI resin

but

when a DI resin becomes depleted, that does not simply mean that the water passes through just as it came from the RO effluent. It may actually be much worse from an aquarist’s perspective. The reason for this is that while the DI resin is functioning properly, all ions will be caught. But when it is depleted, not only the new ions are coming through and might show up in the product water, but so are all the ions that ever got into the DI resin in the first place. The total concentration of ions coming out of the exhausted DI resin will not be raised as compared to the RO's effluent, but which ions are released may be very different.

So I always change mine promptly when it is depleted.

 

[Woodyman]

I have a rather basic RODI question. I have a RO Buddie 50gpd RODI system for my home aquarium. The membrane and sediment cartridges are working well, production rate hasn't dropped). However, the DI cart has completely changed color and is exhausted. My raw feed runs about 400 ppm dissolved solids (I have a water softener on a well). When the DI was fresh, I was getting 0 to 1 ppm TDS in the product water. Now I'm getting 3.

My question is: how critical is this 2 ppm increase? Is that 2 ppm just a percentage of the total mix of TDS (1/2% increase, mostly softener salt) or is that 2% comprised preferentially of more problematic compounds such as heavy metals or organic toxins?

Thanks,

Jay

How critical is the increase?
That depends on your source water makeup and what the components of your incoming TDS are along with ratios of the various compounds. That increase and the dilution factor isn't going to be detrimental for the majority of users.

Is the 2ppm a total mix?
No the di resin will grab the strongly charged compounds over weaker ones, weaker ones previously bound up in the resin can unbind as the resin will bind the stronger compounds.

Weakly bound things would include phosphates and silicates mostly, but others as well. So more than likely you are just allowing more silicates and phosphates through into your mixing/top off water.

 

[vetteguy53081]

2% IMO is not significant but nor is acceptable as it indicates rein is depleted or expired. Generally algae production may occur but not a situation where fish are affected.
Obviously we aim for Zero but zero is literally unobtainable long term. As we know, total Dissolved Solid (TDS) is a measurement of inorganic salts, organic matter and other dissolved materials in water. RO is not a perfect treatment method and is only partially effective at some things like forms of ammonia and nitrate.
TDS is acceptable up to 5 but also an indicator to change all cartridges and resin.
I dont see it being an impact at 2% on your livestock.
Interested to see what Randy thinks

 

[Woodyman]

TDS is acceptable up to 5 but also an indicator to change all cartridges and resin.

Indicator to change resin I agree with.

Not to necessarily change all cartridges. Your sediment, carbon, RO may be fine.

Sure you could change them just because, but you don't need to.

Do you monitor your sediment, carbon, or RO at all?

Monitoring is the way to go to know when to change things, and as stated with TDS coming through it's time to change resin.

 

[Jay Hemdal]

Indicator to change resin I agree with.

Not to necessarily change all cartridges. Your sediment, carbon, RO may be fine.

Sure you could change them just because, but you don't need to.

Do you monitor your sediment, carbon, or RO at all?

Monitoring is the way to go to know when to change things, and as stated with TDS coming through it's time to change resin.

I don't really have a way to monitor the carbon cart. The membrane and sediment I grossly measure by timing the production water - even in the winter with a cold feed it is pretty close to what is was last summer.

Jay

 

[Woodyman]

I don't really have a way to monitor the carbon cart. The membrane and sediment I grossly measure by timing the production water - even in the winter with a cold feed it is pretty close to what is was last summer.

Jay

Sediment you can monitor static or a change in source pressure. Carbon you just want to monitor for chlorine breakthrough, and for RO you should monitor TDS pre and post for rejection %.

If it's been awhile you can change them all, just not the most ideal way to change things.

 

[Woodyman]

I don't really have a way to monitor the carbon cart. The membrane and sediment I grossly measure by timing the production water - even in the winter with a cold feed it is pretty close to what is was last summer.

Jay

RO/DI Basic Guide

There are always a lot of questions regarding which RO/DI setup do I need, how many stages, how do I know when to change filters/membranes, I’m getting a weird TDS value, etc. Hopefully this clarifies a few things and helps some of you out one day. My first recommendation would be to find the...

www.reef2reef.com

 

[HuduVudu]

I have a rather basic RODI question. I have a RO Buddie 50gpd RODI system for my home aquarium. The membrane and sediment cartridges are working well, production rate hasn't dropped). However, the DI cart has completely changed color and is exhausted. My raw feed runs about 400 ppm dissolved solids (I have a water softener on a well). When the DI was fresh, I was getting 0 to 1 ppm TDS in the product water. Now I'm getting 3.

My question is: how critical is this 2 ppm increase? Is that 2 ppm just a percentage of the total mix of TDS (1/2% increase, mostly softener salt) or is that 2% comprised preferentially of more problematic compounds such as heavy metals or organic toxins?

Thanks,

Jay

I had this very problem and scratched my head for quite some time and couldn't figure it out. I started burning resin like crazy. I have an anion and a mixed bed. I would burn both up in two runs of the RO at 65 gallons each. I had moved so I was thinking all sorts of things. I had the BRS chlormine monster, but the water supply was new, and the town I now live in is small. It turns out that it was much simpilier than I thought ... the RO membrane was dead.

Because of what was happening I decided to redisgn my RO system. I added a RO Buddies because I wanted to do a two series membrane to help with waste water. I had moved and water is more expensive here. I had a TDS meter on my old system and I decide that it was stupid to measure input TDS ... it's high, how high ... I don't care. So I am using the meter on the output of the two membranes now so I can see if there is a rise in TDS because for me it is more important to know if the membrane is going bad than to know what the input TDS and the output after the DI TDS.

Just something to consider.

 

[Woodyman]

I had this very problem and scratched my head for quite some time and couldn't figure it out. I started burning resin like crazy. I have an anion and a mixed bed. I would burn both up in two runs of the RO at 65 gallons each. I had moved so I was thinking all sorts of things. I had the BRS chlormine monster, but the water supply was new, and the town I now live in is small. It turns out that it was much simpilier than I thought ... the RO membrane was dead.

Because of what was happening I decided to redisgn my RO system. I added a RO Buddies because I wanted to do a two series membrane to help with waste water. I had moved and water is more expensive here. I had a TDS meter on my old system and I decide that it was stupid to measure input TDS ... it's high, how high ... I don't care. So I am using the meter on the output of the two membranes now so I can see if there is a rise in TDS because for me it is more important to know if the membrane is going bad than to know what the input TDS and the output after the DI TDS.

Just something to consider.

This is another way to do it, the best would be to monitor both so that you replace the membrane when the rejection % is below 96-98 depending on what you choose.

You can also monitor just post for static TDS but keep in mind the seasonal changes. For example if you setup your system in winter and you see 1 TDS Post membrane from November until may then it goes up to 2/3 you might think it's time to replace, but your new membrane ends up putting out the same value. In that scenario you replaced your membrane when it wasn't bad, it was just a seasonal shift in your source water.

Location plays a role in the seasonal shift. Some of us might not see much if any change. While others notice a big difference.

My seasonal shift is ~30-50 TDS. So in the winter months my ROs pump out 1 TDS, but in the summer I see 1-3 TDS.

 

[HuduVudu]

This is another way to do it, the best would be to monitor both so that you replace the membrane when the rejection % is below 96-98 depending on what you choose.

You can also monitor just post for static TDS but keep in mind the seasonal changes. For example if you setup your system in winter and you see 1 TDS Post membrane from November until may then it goes up to 2/3 you might think it's time to replace, but your new membrane ends up putting out the same value. In that scenario you replaced your membrane when it wasn't bad, it was just a seasonal shift in your source water.

Location plays a role in the seasonal shift. Some of us might not see much if any change. While others notice a bid difference.

My seasonal shift is ~30-50 TDS. So in the winter months my ROs pump out 1 TDS, but in the summer I see 1-3 TDS.

This is good to know. I just started using my system this way.

I was just angry (at myself) for not thinking that the membrane was bad. Definitely it would suck on the other side and thinking it was bad and changing it out only to have it produce the same results.

TBF I would really check the outputs unless I started to see a major change in DI consumption.

VERY good information ... thank you for sharing.

 

[Woodyman]

This is good to know. I just started using my system this way.

I was just angry (at myself) for not thinking that the membrane was bad. Definitely it would suck on the other side and thinking it was bad and changing it out only to have it produce the same results.

TBF I would really check the outputs unless I started to see a major change in DI consumption.

VERY good information ... thank you for sharing.

Checkout the guide link I posted above it has more details and covers the other filters as well not just RO membranes.

 

[Woodyman]

This is good to know. I just started using my system this way.

I was just angry (at myself) for not thinking that the membrane was bad. Definitely it would suck on the other side and thinking it was bad and changing it out only to have it produce the same results.

TBF I would really check the outputs unless I started to see a major change in DI consumption.

VERY good information ... thank you for sharing.

Your welcome, I don't have the disease knowledge like @Jay Hemdal, but I know water systems.

 

[Garf]

I have a rather basic RODI question. I have a RO Buddie 50gpd RODI system for my home aquarium. The membrane and sediment cartridges are working well, production rate hasn't dropped). However, the DI cart has completely changed color and is exhausted. My raw feed runs about 400 ppm dissolved solids (I have a water softener on a well). When the DI was fresh, I was getting 0 to 1 ppm TDS in the product water. Now I'm getting 3.

My question is: how critical is this 2 ppm increase? Is that 2 ppm just a percentage of the total mix of TDS (1/2% increase, mostly softener salt) or is that 2% comprised preferentially of more problematic compounds such as heavy metals or organic toxins?

Thanks,

Jay

That 1 to 2% would be made up from whatever elements that are removed by your DI that have the lowest affinity for binding to the resin. Now, what that actually is, is anyone’s guess. That’s a good reason for replacing or regenerating before total depletion.

 

[Jeffcb]

Mine has hovered around 2ppm for about a year and a half on my small RODI unit that I use for top off. My large mixing station I built when I got a larger tank and I use for water changes is still at 0ppm after a year.

I am noticing some hair algae and couldn't figure out why all the sudden its popping up on my 250l. Did an ACP test and all is in spec. Yesterday I check my top off RODI unit and it is at 6ppm. Defiantly time to change the cartridges. Hoping that's what the little patches of GHA are all about... Could and increase of 4ppm cause a GHA bloom ??

On a side note I have an Aquatic Life 75 GPD unit. It is cheaper to buy an entire new unit for 94.88 from Amazon than to buy the cartages separate. Go figure.

 

[Woodyman]

Mine has hovered around 2ppm for about a year and a half on my small RODI unit that I use for top off. My large mixing station I built when I got a larger tank and I use for water changes is still at 0ppm after a year.

I am noticing some hair algae and couldn't figure out why all the sudden its popping up on my 250l. Did an ACP test and all is in spec. Yesterday I check my top off RODI unit and it is at 6ppm. Defiantly time to change the cartridges. Hoping that's what the little patches of GHA are all about... Could and increase of 4ppm cause a GHA bloom ??

On a side note I have an Aquatic Life 75 GPD unit. It is cheaper to buy an entire new unit for 94.88 from Amazon than to buy the cartages separate. Go figure.

Yep silicates and phosphates are weakly bound so they are typically the first things to unbind within the DI resin. So your 4ppm increase could be 4ppm of phosphate, it might not be, but it could be, just depends on what is in the source water and the the concentration within the source.

 

[Jay Hemdal]

Thanks all: I ended up just putting a whole new unit online (cheaper just to buy a whole new RO Buddy system).
Im back to 0 ppm in the product water. I kept the fittings from the old unit as spares.
Jay

 

[Spare time]

ATI allows you to send an icp test taht includes your RODI water. I like to do this but see what exits the membrane before the DI resin to see what exactly is passing through.

 

[Jay Hemdal]

ATI allows you to send an icp test taht includes your RODI water. I like to do this but see what exits the membrane before the DI resin to see what exactly is passing through.

Yep - I do that for my commercial systems at work, but my little home system costs less than an ICP run (grin).
Jay