RO water - Are there benefits to a DI resin kit beyond just reducing the TDS further?

[rdavidw]

Greetings and thank you in advance for your advice.

 

I am pondering adding a BRS resin kit - https://www.bulkreefsupply.com/triple-di-saver-kit-with-resin-and-tds-meter-bulk-reef-supply-bundle.html

 

Are there benefits to a resin kit beyond reducing the TDS further?  If I am getting around 3 TDS consistently from just my RO system would it still make sense to get a DI resin kit?

 

I have a Watts Zero Waste RO system that has been heavily modified.  I am on well water and my incoming TDS is around 148.  I am running a pair of membranes in parallel and use a normally open solenoid valve to bypass the flow restrictors on the brine line.  When the pressure switch hits 50 psi the pump turns off and the inlet solenoid closes and the bypass solenoid opens and drains into a floor drain, de-pressurizing the membranes.  When the system powers back up the bypass closes and the brine line is pumped back into the house water further upstream.  It only waste about a cup of water down the drain each time the system cuts off and its all automatic.  Works great, with the bypass flush I am getting very little TDS creep.  I am getting about 2 or 3 TDS at start up and it climbs to about 7-9 TDS and will then gradually fall to 1 TDS.

 

I have a pair of 25 gallon pressure storage tanks that are plumbed together.  I use the RO water for a top-up reservoir and 50 gallon water change reservoir for a 150 gallon reef tank.  I also use the system for a home brewery and have a drinking water line throughout the house.   I have a re-mineralization stage before the storage tanks on a 1/4" line, everything after that is on 3/8" tubing.  After the storage tanks I have a polishing carbon stage and a 25 watt UV.

 

If adding a DI kit would be a noticeable improvement for my reef tank, I am guessing that I would not want to have it on the high flow 3/8" line after the storage tanks.  I am also guessing that I don't want to use the DI resin kit on my drinking and brewing water?  I could make one of my two 25 gallon storage tanks just for the reef tank so it would go RO --> DI stages --> storage tank # 1 --> reef tank.  The other line from the RO would go re-mineralization stage, --> storage tank #2 --> polishing stage --> UV --> brew kettle and drinking water.

 

Thanks!

[DaJMasta]

I'm not sure I have a full gauge on your system, but I think there could be some benefit, though probably not a pronounced one, to adding a DI stage for your reef tank.  On well water, you're not worried about excess chlorine or chloramine getting through the RO stage, and since your TDS output is low, the DI stage is probably less important than on other systems, but reducing TDS to "0" means a lot less buildup in the system from ATO additions, in particular, and especially if you don't do frequent water changes.  If you're doing weekly water changes, don't top off a huge amount, and aren't seeing nuisance algae or other problems, then the different may not be tangible.

 

If you do add a DI stage, yes definitely before or around any remineralization stages, and if you're going to use the output for drinking or cooking, I've heard the taste is not great unless you have that final carbon polishing stage (which you have, so maybe is fine?)  I would probably leave it on the reef line specifically just because you're going to use it up a lot less quickly with less flow through it and it probably will be no benefit to the other applications - which I think is the proposed setup you mentioned.


With that level of TDS, though, I would say it's probably not worth it unless you rarely do water changes (<1 per month or so), you need lots of ATO water added, or you are seeing some algae or similar that has stubbornly persisted and you think it could be nutrient adding through water.

[rdavidw]

10 minutes ago, DaJMasta said:

I'm not sure I have a full gauge on your system, but I think there could be some benefit, though probably not a pronounced one, to adding a DI stage for your reef tank.  On well water, you're not worried about excess chlorine or chloramine getting through the RO stage, and since your TDS output is low, the DI stage is probably less important than on other systems, but reducing TDS to "0" means a lot less buildup in the system from ATO additions, in particular, and especially if you don't do frequent water changes.  If you're doing weekly water changes, don't top off a huge amount, and aren't seeing nuisance algae or other problems, then the different may not be tangible.

 

If you do add a DI stage, yes definitely before or around any remineralization stages, and if you're going to use the output for drinking or cooking, I've heard the taste is not great unless you have that final carbon polishing stage (which you have, so maybe is fine?)  I would probably leave it on the reef line specifically just because you're going to use it up a lot less quickly with less flow through it and it probably will be no benefit to the other applications - which I think is the proposed setup you mentioned.


With that level of TDS, though, I would say it's probably not worth it unless you rarely do water changes (<1 per month or so), you need lots of ATO water added, or you are seeing some algae or similar that has stubbornly persisted and you think it could be nutrient adding through water.

Thanks DaJMasta!  I do occasionally get some spots slime algae and run some GFO to knock it out.  I only do a 50 gallon water change every three months.  I think I will try it out, not very expensive and it will save my re-mineralization stage by isolating it to the drinking water side.   

[JMsAquarium]

As DaJMasta mentioned, in a well, you should have none or almost no chlorine/chloramine. The purpose of the DI resin is mainly to remove those. Which is a must have when the water source is from the city

[AlanM]

This is a bit older thread, but one thing to be concerned about on a well is lots of CO2 in the water can eat up one of the two components in a mixed cation-anion resin.  I forget which.  Tom @Origami has dealt with well water before and can give advice.

[Stephen]

1 hour ago, AlanM said:

This is a bit older thread, but one thing to be concerned about on a well is lots of CO2 in the water can eat up one of the two components in a mixed cation-anion resin.  I forget which.  Tom @Origami has dealt with well water before and can give advice.

CO2 eats up the anion resin.