Reverse Osmosis Filtration System To Lower pH

Discussion in 'Reverse Osmosis Filter for Freshwater' started by jcmguy, Aug 3, 2014.

  1. jcmguyValued MemberMember

    So I bought a reverse osmosis system from a friend who said he didnt need it anymore. It is a 3 stage filter that had this in it for a membrane:

    Should I buy another on of these to replace and get the replacement prefilters or should I get another type and if so, suggestions please?

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    I need it to lower the TDS to close to zero.

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    Last edited by a moderator: Aug 3, 2014
  2. jcmguyValued MemberMember


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  3. LinwoodValued MemberMember

    I'm new to this but did a lot of research on RODI and PH and for what it is worth....

    You only need to replace the prefilters and membranes if you need to. Sorry, but there's no good way to know, and they are pretty pricey. The first thing I'd do is get a TDS meter, if you don't have one, so you can tell.

    Secondly, if this is a drinking water system (as opposed to aquarium) make sure it does not have a post-filter for remineralization. if it does, remove it.

    If the membrane has dried out (and was used) it may be bad. Recommendations are to keep them moist.

    My suggestion is hook it up and see what you get out of it. Flush the membrane well (does it have a flush setup? If not, just remove the flow restriction on the waste), then after flushing restore the waste flow restrictor and let it run 10 minutes or so in normal mode, and then check the water coming out. TDS should be > 90% removed relative to input, generally more like 95%.

    If I didn't know anything about the history of the filters, I'd probably replace the carbon and sediment filters (try for something quality, like 1 micron, saving money there costs you more on membranes). Then try the membrane again. if it still isn't filtering adequately you need to replace it.

    You can't get TDS to zero with RO only for most tap water, 5% of input TDS is probably a good normal estimate. But that's awfully low.

    Note that this does NOT really lower PH. Well, it does, but it also removes all the buffering so what you are left with is rapid, erratic PH swings. If you are trying to lower PH with RO, you might look at something like seachem alkaline buffer and acid buffer.

    use alkaline buffer to get the desired KH (based on what you have in the tank), and then add the proportion of acid buffer to get the desired PH (the recipie is on the bottle, e.g. 2:1 gives ph 7.0, 1:1 gives ph 6.0). If the TDS is really low consider something like equilibrium for bringing GH back up a bit and restoring essential minerals. Pure RODI water is too pure, even pure RO water if your input water is not bad may be too pure.
  4. jcmguyValued MemberMember

    Thank you!! I am going to be putting red Jewels in the tank and someone suggested to me that I use this system. I'm going to instead purchase a complete 6 stage aquarium system that lowers the ppm to 0. They say the water is fine to just go right into the tank from there. Is this wrong or should I still do the additives you suggested?

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  5. LinwoodValued MemberMember

    From everything I have read it is not healthy to put RODI water directly into the tank for initial fill or for water changes, for two reasons: (1) it has no natural buffers so you will get wide PH swings which are not good for the fish, and (2) it lacks essential minerals, that need to get back in from somewhere.

    For top-off due to evaporation you put it in without modifying (since what evaporated was also mostly pure water).

    What I understand for fresh water is you do two things: You add some form of essential minerals (I use Seachem Equilibrium but that's more for planted tanks), adding enough of it to a desired general hardness (GH).

    Then you add an alkaline buffer (I use Seachem) to get a desired Carbonate Hardness (KH).

    You determine the desired GH and KH by what kind of fish or other stock and/or plants.

    Then you add acid buffer (again I use the Seachem product of the same name) in a specific proportion to the alkaline buffer to get your desired PH (again, based on your stock). For example, to get ph of 7.0 you put 2 parts alkaline to 1 part acid.

    I mix mine up in 5 gallon jugs -- I put 1 teaspoon Equalibrium, 1/4 teaspoon acid, 1/2 teaspoon alkaline for each 5 gallons. So the quantity is really quite small you are adding back, a jar lasts a good while.

    It is interesting to note my tap water has TDS of about 370. Out of my RODI it is zero. When I finish mixing it is about 330. Makes me wonder at times. But I know what's in the 330.

    The water chemistry I think I've figured out somewhat -- what you need for each fish like the Jewels I have no clue. Sorry. :)
  6. ricmccWell Known MemberMember

    You can add Seachem's acid and alkaline buffers to RO/DI water to arrive at specific hardness and therefore buffering value (and they are both very good products), but I find it easier to just mix in some pure tap water to basically do the same thing.
    I use a 50 rain collection pail to collect my RO/DI water.
    However, if you use the adding tap water method, it is quite easy to just fill a 1 gallon container with RO/DI water, remove a small amount in a measuring cup and replace with an equal volume of tap water until you arrive at the values that you want.
    You then just work out what ratio of tap water you used in the 1 gallon container, and apply that ratio to however much RO/DI treated water that you wish to use.
    Far easier if you mark the collection pails in into whatever units use find convenient to use, 1 gal, 5 gal, etc
    Of course, if you are handy with your maths, it is also very easy to measure your tap pH, GH, and KH. and assuming that your RO/DI unit will produce 7.0, 0, 0, waters, just figure out on a piece of paper what ratio of tap water to RO/DI water will give you the values you want.
    I am hoping that that was somewhat clear:)-----rick
    Last edited: Aug 26, 2014
  7. paulddsNew MemberMember


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  8. paulddsNew MemberMember

    That last reply was an error in typing ability.........

    My real reply is a question about RO water usage.


    I have a well for water. Misled about the quality of the water system when we bought the 4 year old house.

    Super fine sand would load a paper filter in a day and had to replace 4 year old faucets and valves that were destroyed by grit and almost lost my 4 year old electric water heater due to buildup in tank and hard water damage to elements

    I had Kinetico set up a system for my whole house for filtration and a system to soften the hard water (real common problem in central PA)

    I also added a uv sterilizer for all the water.

    I did then have a RO system added for drinking water at sink.

    Had not had a tank for about 30 years and thought with such quality water system I would set up a tank my son had left in "storage" in my basement. Have 3 young grand kids and I remember an uncles guppy tanks when I was a kid. "Big funs" like my son used to say

    I set up my tank (29 gallon freshwater) with all RO water, learned about cycling the tank the hard way, but now I understand and have good ammonia and nitrite tests regularly with occasional higher nitrates that are much better as I have started to add plants and regular water changes

    Recently i had some ich problems, and used the forum and am almost two weeks in to raising the water temp to 86 to treat to avoid adding meds or other chemicals. Nice clear water. Fish (5 platy's, two small bristle nose pleco (plan to move one to a 5 gallon tank with one betta I just inherited from my granddaughter,she won as a table ornament at a child's party in a flower vase!!), two small albino cats, school of 9 of small golden little tetras and 4 ghost shrimp) look good

    I do weekly gravel vacuming with partial water changes because of the load of fish ( I realized i had starved two small pleco and now tend to use more food to be sure the bottom guys get fed. I do all of that with "pure" RO water.

    I thought with RO water, I was really doing good stuff for my fish.

    Never paid any notice to ph and other parameters since I thought RO water was great.

    Now trying to educate myself about ph balance, buffer capacity, mineral replacement hardness etc.

    First what testing equipment would be good to use and when would you test (I have been using an API liquid master master kit but only includes ph and high range ph tests in this kit ).

    Second any suggestions for posts and/or articles on the forum would be helpful to get me started.

    Third I like the idea of using RO water because I am starting with "pure" water that I can control parameters.

    Looking forward to following this thread

    Thanks in advance......


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  9. LinwoodValued MemberMember

    The primary issue with using "pure" RO water is that trace minerals that may be important to fish (or plants if you have any) may be missing. These tend to affect stock and plants over long time periods; it is not like chlorine or a poison where you see them die quickly, it is more a case of them failing to thrive over time (if you have this problem).

    Unlike RODI water, RO water does still have some mineral content. Drinking water RO water often has a lot -- some systems actually add a "filter" at the output to remineralize water so it tastes better.

    First thing I'd do is find out if that's true on yours (I am understanding you are using your drinking water RO system for the tank, right?). Either look at it, or get a TDS meter (about $25 for a very good one, some are cheaper). This gives a broad indication of how much "stuff" is in the water you are using, though it gives no indication of what that stuff is.

    Typical RO water may have 10-20 ppm on a TDS meter. A bit higher and it indicates your RO system may need maintenance, a lot higher and either it's just broken or you have something already remineralizing the water.

    RODI water is definitely a bad idea alone; it has a TDS reading at or near zero. RO water not so bad, but probably not good, and may depend a bit on the fish you have.

    If I were you, I'd also pick up a KH/GH test kit (API makes one as well). It's pretty cheap, slightly redundant to the TDS meter but the TDS meter is so fast and handy I'd recommend one anyway. The test is just to add a drop at a time until a color change occurs, the number of drops is the "degree" of KH or GH.

    KH is carbonate hardness, and is largely a buffer. Very low (e.g. 1 or less) of KH and you are likely to have significant ph changes which can stress the fish. Extremely pure water also makes your ph test kit less accurate, e.g. RODI water is ph of 7, but it has so little buffer a bit of air exchange can drive it easily to far more acid or base.

    GH is General Hardness and represents other minerals as well. If you look at profiles of your stock, it will tell you what ph and hardness ranges they are most comfortable in. For most aquarium-friendly fresh water stock they can live in a wide range of ph and hardness, but getting somewhere in the right neighborhood is good, and fairly easy.

    If you find you are anywhere near the right neighborhood with your RO water as is, I would do nothing. E.g. if yours is 2 and your fish are best in 3 or 4 - fine.

    If you find you are way too low, and want to raise it, the easy solution is get some Seachem Alkaline and Acid buffer (two different powders). You mix a tiny amount of them together and add to water change RO water to change KH.

    The way to think of it is this -- follow the directions on the Alkaline buffer to get the KH you want. For example, I add 3/4 teaspoon to each 5 gallons. Then look at the acid buffer table and get the right ratio for it based on desired PH. For example, to gt a ph of 7.0 you then use half as much (by volume) of the acid buffer, so I use 3/8ths teaspoon.

    This also gets you some GH, but if you want more get a trace mineral supplement as well. I use Seachem Equilibrium which is nice for plants. This is harder to dissolve by the way, and takes a bit more usually.

    KH being a bit higher makes PH more stable (and also as it gets much higher makes it hard to get PH down low).

    Raising GH with something like Equilibrium is more about having trace minerals, and doesn't directly affect PH.

    These do not need to be precise at all. dKH of 3 or 5 or 7 are all likely to be fine for most fish. Extremes are bad however, and zero is one extreme.

    One final note on numbers -- dKH and dGH is a linear scale, so twice the "stuff" is twice the number. PH on the other hand is a log scale, so the difference in ph of 8 and 7 is that 7 is TEN times as acidic.

    By and large stock can accommodate wide variations in all of these parameters, but cannot tolerate quick swings. So if you do decide to start making up water of a specific type, adjust slowly with either small water changes, or work your way up in how much you add.

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