From The Archives: Friday Morning Quick Tip #30: The Horizontal Position Isn’t Advised

I’m a big fan of  using Reverse Osmosis DeIonized (RODI) water for your saltwater tank.  And if your RODI unit has a certain stage in the horizontal direction, it needs fixing


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Comments for this article (28)

  • Michael says:

    What would be the best method to test the water quality between the two setups? I have a horizontal DI bed, much like the one you displayed, and the water always appears to fill up the entire medium. I can see that if you don’t have the proper amount of water pressure, or medium in the DI that it may not be utilized properly.

  • Brian says:

    So does that mean the Coralife RO/DI is a bad design, their entire line is built with the DI horizontal?

  • Binnemann says:

    ‘m Also a big fan of the reverse osmosis system.
    Without which it will not be easy.
    mfg Bernd

  • Josh says:

    I have a TDS meter to test mine, it has a probe after the RO module and one after the DI.

  • RICH says:


  • Michael…the issue with the horizontal bed isn’t so much about quality of water as both a vertical and horizontal bed can yield 0 TDS water. However, a horizontal bed won’t last as long as the water passing through it can come in contact with less media, causing the media that is in contact with the water to exhaust quicker. The result will be parts of the media that aren’t exhausted, yet the water coming out of the DI bed won’t be 0 TDS

  • Chris says:

    Do you have a list of companies that make rodi units that do not have a horizontal bed?

  • Chuck says:

    Great tip mark. Never even crossed my mind that the ‘filter experts’ who I bought my RO/DI setup from would sell a horizontal DI design that helps sell more DI media… go figure. I’m thinking rather than completely replacing the horizontal-style design (I’ve got the same you showed in your video) it could easily be re-plumbed to sit vertically… would only take a few fittings and tubing, and a clever way to hang/mount it. Thanks for all the great tips over the years — Keep up the good work! This one will definitely be put to good use on my system asap.

  • Postaldave says:

    Can you just rotate up the one you have or do you need to purchase a vertical designed one?

  • Tina says:

    If I have a 5 stage system with a horizontal bed, how would I retrofit it with a vertical bed? I do notice it goes through resin (especially if I don’t pack it thoroughly).

  • Dave says:

    Hey Mark,
    I have a TDS meter and since I installed a booster pump I am getting more life out of my DI resin not to mention all the other filters. My question is what is an acceptable TDS level before I change my filters? Presently I have a reading of 2.

  • Dave..if your TDS is above zero, then I’d start by changing the DI resin. Then move onto the other filters.

  • Postaldave & Tina…I’ve had mixed success rotating the horizontal beds vertically. Even with the pads at the ends of the filter, the media still escapes and the DI resin doesn’t last as long. I recommend replacing the horizontal DI bed with one designed to be vertical.

  • Adam Blanden says:

    Great tip! The issue with the DI column is essentially in the media packing. One of the primary things my laboratory does is protein expression and purification — so I’ve run hundreds of chromatography columns. Even when you pack a column vertically, you have to be careful about making sure the bed settles evenly and that you don’t force little “paths of least resistance” through it that the solution can flow through (a phenomenon called channeling) — the difference in efficiency is pretty striking, and that’s just with little channels, that alone with the column horizontal! Kinda makes you wonder who thought that was a good idea…

  • Bob says:

    I have SpectraPure FR-25, 25 gallons per day. It has 3 vertical filter chambers one 1 horizontal chamber on top, SpectraPure® Maxpure 25 GPD RO/DI System, is this a vertical or horizontal unit? Thanks, Bob

  • dave from brooklyn says:

    My tds still reads 0. My parameters are good. My water here in NY is pretty good. Would you st change the redin after a year?

  • Joe says:

    So are you saying if we have a model with a horizontal bed that can not be made vertical we would be better looking at a new system? Mine is a compact system from a known company that cannot be changed.

    System would still work but in the long run would cost you more money replacing filter more frequently.

  • Big Mike says:

    Hi Mark. Thank you for all your tips and advice. They have been a great help the last year which is my first year in the hobby. Here is the situation. I have a 75gpd BRS 5 stage RO/DI system that I bought a little over a year ago. My TDS reading as of today is 3 ppm. The unit came with the color-changing DI resin and the center 3 inches hasn’t really changed color yet, at least not like the top and bottom. I am just wondering if you change the resin out as soon as it is not 0 ppm any more or do you have a certain number you will wait to reach? In one of Vivid Aquariums videos Dave says he waits until 10 ppm before he will change DI resin and filters. I do not have nuisance algae growing any where and the tank’s parameters have been excellent. Thanks again for all the videos you have produced. You have made this hobby really enjoyable. My first couple months were rough. I made a ton of rookie mistakes. LOL!

  • Rick Schmidt says:


    My RO/DI unit has a horizontal DI bed; but with a few pieces of tubing and one extra connector I can McGyver it into a vertical position. My question is whether my inlet to this stage should be on the bottom or the top of the cartridge.

  • Sean says:

    Do you run stereilizers on your tanks. Have you done a clip on them?

  • Sean…I don’t recommend sterilizers.

  • Rick…inlet should be at the bottom.

  • Big Mike…I change out my resin whenever the TDS of the water coming out of it is anything more than zero. The cost of DI resin is much cheaper than dealing with an algae issue that might get caused by using your DI media until the TDS reaches a higher number.

  • Joe…you can easily add on a DI vertical stage for not a lot of money. Once the DI resin in the horizontal stage runs out, you can just leave that stage empty.

  • Dave…I change my DI bed whenever the TDS of the water coming out of it reads over zero. If that takes 2 years, then great! If it takes 3 months, out the resin goes. Every year I change out the rest of the DI filters (not the RO membrane) though regardless of the TDS reading. It’s much cheaper to change out 3 filters than to deal with any headaches that could be caused by bad RO filters.

  • Bob…the vertical chambers are likely the sediment and carbon block chambers, not the DI chamber. The DI chamber will be filled with a media that is probably brown or blue and this media will probably change colors as it gets used up

  • Adam…great point and a great time to remind people of this quick tip I made on the same subject.

  • Steve Dodd says:

    Hi Mark , how can I email you to ask a few questions , Im not on twitter , (or twatter as we call it here in the U K) , or facebook and have no desire to be , but i cant find a contact for you outside these two.
    could you let me know
    Steve Dodd

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