How low can a single DI filter lower TDS after RO?

[kliv555]

So after countless hours, I finally have my RODI and mixing station setup for my first 120 gallon reef tank. After running the RODI system, I am getting a TDS reading in the 19-22 ppm range, which is after the RO but before the DI. I am wondering before I 100% lock this permanent installation down, should I be adding another DI filter to help with the TDS or should 1 TDS filter be sufficient for this TDS number? I have been unable to find anything in previous threads about how high of TDS a single DI filter can actually

I have a aquafx 200 GPD barracuda octopus, as well as 2 prefilters, which only have a 5 and 1 micron filter in them. I have debated moving one of these filters to the product water side as another DI filter. I could also add another carbon prefilter if that would make a difference.
I live in nowhere rural Canada and am off a well supply. Back when the well was first dug, I had a water sample of 1200 TDS, now this should be much lower as the well had never been flushed or ran yet. Coming into the house I have a large iron filter and water softener. I’m guessing my TDS going into the RODI is in the 300-600 range.
Any comments greatly appreciated.

 

[Freenow54]

Do you not have a TDS meter downstream of the DI?

 

[Freenow54]

Secondly before I added the DI my TDS was about 6-8 My water comes from Lake Erie. Had to change my media at 7 months, and was making water only for Aquariums about 120 gallons in 2 weeks. Just so you know you can buy media on Amazon fairly cheaply. I think I would add another filter upstream with even finer microns

 

[LeftyReefer]

I would add more DI capacity... or better yet, a second RO membrane to get your TDS down lower.

Feeding 20 TDS water into your single stage mixed bed DI resin is going to exhaust it pretty quickly.
You will be going through lots of DI resin doing that. I would think it would pay off to add another RO membrane if it will get your TDS down into low single digits before your DI stage.

do you know if your well water is high in dissolved CO2 ?

 

[NowGlazeIT]

I went from 3ppm to 5-6 when I changed out my RO membrane.. I thought that was bad but 20!? You will definitely go through a lot of DI resin. A single Dow membrane has the potential to remove 98percent of your freshwater’s tds. If your using a standard brs rodi or something similar then check your incoming tds. If it’s not near 1000 then I think somethings wrong with the membrane or the setup.