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Thread: RO/DI system question

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    kerry's Avatar
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    RO/DI system question

    I have a question about DI filter replacement. At what PPM do you guys change the DI filter media? Mine has just started to read 1-2PPM TDS. I am only using it for top off as you all now I have scrubbers so I dont water change. My tanks (all three) usually need about 4-6 gallons per week for Kalk top off. Is 1-2 PPM TDS bad enough to change the DI media?
    150G. Reef/Mix
    125G. 3 Regular Oscars/1 Jack Dempsey
    75G. 20+ Africans
    40G. Fish/Reef. Algae Scrubbers on ALL my SW
    10G. SW Fish/Reef.
    10G. SW Hospital/new fish quarantine/pod breeder tank
    6 stage RO/DI system 200 GPD.

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    Change the DI. Anytime you get a 1+, the DI is spent. Yes, 1 TDS is considered "bad". The reason being is at 1 TDS, you know some bad stuff it making it all the way through the filter, and you have no idea what it is. It could be benign like calcium, or could be bad like copper or other nasty chemicals. It is the "unknown" aspect that makes any TDS reading become questionable, and in this hobby, water is not something you really want to have to question and worry about if you can help it.

    General rule of thumb for RO membranes is 10% of what the tap water TDS is. If your tap water TDS is 500, the water coming out of the RO membrane should be no more than 50 (90% rejection rate), ideally more like 25 (95% rejection rate). If the water coming out of the RO membrane is above 10% of what your tap water reads, that means it is time to replace the membrane. Back flushing the membrane extends the life by A LOT, and a $10 flush kit from Bulk Reef Supply is a must have, makes it so easy to back flush the membrane in seconds, which I do before and after every time I run my RO/DI filter. You can keep a bad membrane and just replace DI more often, but that ends up being more costly in the long run because the DI resin will get spent fairly quickly if it has a high TDS going through it.

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    Thats what I had been doing, when it got to 1 I was changing it. It takes about a year to get to 1 PPM as I have pretty decent water out of the tap, if I remember correctly it was 32 or 42 PPM out of the tap or maybe that was out of the fridge that has one of those cheesy carbon filters in the water supply line which I cant imagine removes much TDS anyway. Before the DI the RO is 4 PPM.
    150G. Reef/Mix
    125G. 3 Regular Oscars/1 Jack Dempsey
    75G. 20+ Africans
    40G. Fish/Reef. Algae Scrubbers on ALL my SW
    10G. SW Fish/Reef.
    10G. SW Hospital/new fish quarantine/pod breeder tank
    6 stage RO/DI system 200 GPD.

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    My water out of the tap is about 450us. I recharge when DI reads 1us. I've read somewhere(something to do with RHFarley) that as soon as DI is spent, all types or nasties are released.

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    What happens with DI is spent is that certain ions have a greater ionic strength than others. So if there is unused DI media available, all is good. Once the media is fully used, whatever ions have a weak bond will be released when something else with a stronger bond comes along. IIRC the things that get released are high up on the list of what you don't want released. Ammonia and phosphate come to mind, but I can't recall exactly.

    What I will be doing shortly is adding a second DI chamber to my setup. This way, I don't have to wait until one is mostly used up but not completely. I can just wait until one is completely used, then switch the DI out on that one and switch the canister order or just replace the beads in the first one whenever I get a chance, either way no chance of my DI burning out

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    Quote Originally Posted by Floyd R Turbo View Post
    What happens with DI is spent is that certain ions have a greater ionic strength than others. So if there is unused DI media available, all is good. Once the media is fully used, whatever ions have a weak bond will be released when something else with a stronger bond comes along. IIRC the things that get released are high up on the list of what you don't want released. Ammonia and phosphate come to mind, but I can't recall exactly.

    What I will be doing shortly is adding a second DI chamber to my setup. This way, I don't have to wait until one is mostly used up but not completely. I can just wait until one is completely used, then switch the DI out on that one and switch the canister order or just replace the beads in the first one whenever I get a chance, either way no chance of my DI burning out
    I recharge my DI with HCL and sodium hydroxide. The beads are good for at least 2 years. However, I work at an electrophoretic paint deposition plant and I can get my hands on these chemicals easily. I can see how things may become more complicated if these chemicals are not readily to hand. Recharging only takes 2 hours tops.

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    I thought you had to have your DI separated out into cation and anion to be able to recharge. I use BRS nuclear color changing resin, it's cheap and lasts long anyways (since i only use it for top-off water, no PWCs)

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    Quote Originally Posted by Floyd R Turbo View Post
    I thought you had to have your DI separated out into cation and anion to be able to recharge. I use BRS nuclear color changing resin, it's cheap and lasts long anyways (since i only use it for top-off water, no PWCs)
    Separate by adding 16ish % sodium hydroxide. The anion will float after a while. If it doesn't drain the solution and add some more sodium hydroxide. Separate the anion and cation (pour the anion into separate jug). Rinse the cation very well till all traces of hydroxide are gone.fill the cation jug with 16%ish of hydrochloric acid. This will recharge the cation beads( stir every 30 mins for 2 hours ). Rinse both containers with r.o. ( I suggest 10 litres of rinsing, 1 litre at a time ). Ther are detailed methods of D.I. RECHARGING if you google it.

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    Floyd, not sure which way you were thinking of using 2 DI canisters but my experience is I have not had good luck with using 2 DI containers back to back, they seem to both go bad within days of each other. I believe the reason is once the first DI container is all used up, you get all that nasty stuff then being released from the first DI canister and dumping into the second canister, which makes the DI resin get used up VERY quickly. I have found it much better to only have 1 DI and have an inline TDS meter and have a second canister loaded and ready to go so when I do see a 1 TDS I can swap out the canister in a few seconds. That may be the way you were describing doing it, just wasn't sure so wanted to share my experience.

    I will skip on recharging, I am not comfortable enough playing around with those chemicals all over a couple dollars worth of DI. If a person has access to the chemicals and comfortable doing it, by all means go for it, just not for me.

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    To me that makes no sense, but I guess I haven't tried it before. Theoretically, using 2 DI canisters would be exactly the same as one larger one. In mine, the resin changes color from blue to brown when it gets used up. The brown separates into 2 distinctly different colors and one sinks to the bottom, the other stays in the middle, and the blue unused resin stays at the top. So the water passes through the used resin first, which would 'release' the weaker ions and those get picked up by the unused resin at the top. When this is used up, the released ions would just go to the next DI canister like it was more media in the same canister. So what am I missing?

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