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Well this is a little embarrassing...

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For the past three months, my reef has been suffering from elevated phosphate levels. I've never had such a roller coaster, with the numbers rising and then falling as I treated to drop them again. Last night I did a lot of water testing.

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a) First I tested the 215g reef to check the levels.
b)Then I checked the 400g that is full of water, sand and live rock to know if the parameters were close enough for livestock transfer and to make sure it wasn't cycling. The rock had been exposed to air for nearly a week.
c) Finally, I tested the 250g of newly mixed saltwater in the poly tank since it was a completely different brand of salt.

Using the Hanna Low Phosphate Checker, I was really surprised to see PO4 in the new batch of saltwater. I could understand it being in the 400g since the rock might leach out PO4, although it has been in water circulation for more than three years in a barrel without any food whatsoever. Doubting that a new batch of salt would contain PO4, I decided to test the Phosphate level of the RO/DI water. Testing it twice in the past 12 hours, I got measurements of .06 and a measurement of .09 with the Hanna Checker.

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Now that I'm aware of the source of the phosphate (which wasn't my feeding at all, but rather via top off water daily as well as through water changes), I need to resolve it. I'm going to do some more testing, but my initial thought is that perhaps I'm running my RO water too quickly through the DI resin. I have three membranes with booster pumps running into the DI stage at 0.3-gallon per minute. Normally a 100gpd system runs at 0.06-gallon per minute through the resin, and 150gpd equals 0.1-gallon per minute. Adding a second DI isn't cost-effective nor a solution, as the first DI can fill up and later leach back out into the second DI's resin, wearing the second one out more quickly. With high flow rates, water can channel through the DI resin instead of flowing over all the beads individually.

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The filters are two months old, the DI resin less than a week old, TDS measures 0. The membranes are about 14 months old. The TDS prior to the DI is 16. So, that leaves flow rate as a probable cause. Like Tim the Toolman, I figured more power is always better but I may have discovered a drawback.

I can't believe I didn't think of this sooner. Since we want our reef's water to measure at .02 or less, adding water that is nearly .1 everyday is problematic. I'll be sure to update you with what I discover.

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Updated 10-24-2013 at 03:52 PM by melev

Water Chemistry


  1. Reefski's Avatar
    with levels 0.26 in the 215 how are the corals growing and how is the color?

    that is very interesting. something for us all to check.

    what are some guidelines as to when to replace the RO membrane?

    remember the tester has an accuracy +/- 0.04ppm
  2. melev's Avatar
    The membranes can be verified for health these ways:

    1) TDS - what is the TDS after the membrane prior to the DI, and has this changed from previous measurements? If it used to come out at 9, and now it comes out at 70, the membrane is very likely done.
    2) Waste ratio - Has the waste ratio changed dramatically? If it was 4:1 (4 quarts waste to 1 quart product/good water) before, and now measures 10:1, the membrane needs to be replaced.
    3) Output - Have production rates plummeted? If the water no longer comes out like before, it could be plugged up.
    4) Visual inspection - Has the membraned telescoped and/or has the rubber band traveled down the membrane's length like this one? This one suffered both issues:

    This is a new one by comparison:

    My corals look healthy overall, considering the soup they've been enduring. I posted a blog a few days ago with pictures.

    I dosed Phosphate Rx last night so the reef should have less PO4 than yesterday. I'm burning through low-test reagents with all the testing I've been doing. I treated the 400g as well.
  3. melev's Avatar
    I did more testing tonight to see if I can determine where the PO4 is coming from.

    TAP water: 216 TDS

    150gpd system with booster pump. Membrane 1 year old, filters two months old, DI less than one week old:
    PSI: 68

    Temperature: 76F
    Estimated flow rate: .1 gal/min
    RO water: 31 TDS with HM2; 19 TDS with HM1 (I may need to calibrate my HM2's probe)
    DI water: 0 TDS with HM2; 0 TDS with HM1
    Phosphate measured in DI water: .06

    300gpd system with booster pump. Membranes 14 months old, filters two months old, DI less than a week old:
    PSI: 75

    Temperature: 76F
    Estimated flow rate: .2 gal/min
    RO water: 23 TDS with HM2; 16 with HM1
    DI water: 0 TDS with HM2; 0 TDS with HM1
    Phosphate measured in DI water: .1

    To measure the DI water, I emptied the housing of any water, then shook out any water in the DI resin until the cartridge was essentially water-free. Reinstalled cartridge and turned on system to produce RO water first, then flood the DI section and let it run for a minute before measuring.

    Flow rate seems to indicate that PO4 is passing through seemingly mathematically, although the value didn't double.

    That's it for tonight.
  4. cyano's Avatar
    What is the PSI difference with and w/out the booster pump? It is extremely plausible that you are running too much pressure through the membrane, in fact if PO4 is leaching through the membrane there is even a chance that chlorine is also getting through your RODI system. When I was in the military I used to run a ROWPU system which in essence is an oversized RO-DI system. With that system depending on water conditions, booster pump PSI, and the salinity of the water there was a maximum GPM that we could run through the system to maintain optimum performance.

    I would disconnect the booster pump all together and retest the PO4 in the RO water after running it at a lower PSI for about an hour.
    Updated 10-25-2013 at 02:01 PM by cyano (adding)
  5. melev's Avatar
    The difference in pressure with the booster pump is about 15 PSI. My home's water pressure is about 60 out of the wall.

    Thanks, I'll do more tests.
  6. dahenley's Avatar
    75psi is nothing.....
    i have 80+ psi from the tap... and up to 90 some nights when usage is low in the neighborhood.

    membranes say they need 65psi min for the estimated GPD ratings.

    if you unhook the booster, test it after it makes a decent amount of water, but then i would bump it to 85-90. i know the clear housings are rated for 110psi i believe. but because you have the dual membranes, (and depending on if they are in seriens or parallel will depict on what psi is going into each...

    its a long shot, but its a 10 min adjustment, and about an hours worth of run time before getting a flush in the system before reading the new numbers.
  7. melev's Avatar
    What I did was change out everything last night. I changed out the membrane, all the pre-filters, and ran it for an hour to flush out the food grade preservative. Then I hooked up the new DI resin section and ran it for 10 minutes.

    Using only the 150gpd system with the booster pump:
    Water temp: 76F
    Water pressure: 72 PSI
    TDS going in: 143
    TDS after the RO stage: 20 (HM2) and 18 (HM1)
    TDS after the DI stage: 0 (HM2) and 0 (HM1)

    PO4 after RO stage: .03
    PO4 after DI stage: .08

    Which makes no sense.
  8. melev's Avatar
    Today I decided to do one more test. I added another housing after the DI, and inserted the DI cartridge that was less than a week old (and had processed 150g of water last week for the storage tank).

    Ran the 150gpd boosted system for a few minutes, and then collected my samples:
    Water pressure: 72 PSI
    Temp: 76 F
    RO TDS: 13 and PO4: .02
    DI TDS: 0 and PO4: .12

    Two days ago, TDS was slightly higher, as posted yesterday at 2:13pm ^^

    So it seems to me that if you added a second DI onto the first DI, and if that resin is releasing what appears to be measurable phosphate, that would explain why I'm getting a .12 ppm reading tonight.

    Ironically, I have the choice at this time to use RO water with slightly higher TDS and lower PO4, or use DI water with no TDS and higher PO4.

    I'll update when I know more, and why this is happening.

    In the meantime, the Reef is measuring at .13ppm and the new 400g at .37ppm so I'll be dosing Phosphate Rx tonight to get that down.
  9. dahenley's Avatar
    i would run the RO with less phosphate and more TDS (TDS isn't a measurement of bad stuff, its just a measurement of stuff. (good and bad)) TDS readings include minerals,calcium,magnesium and what not.

    well, ill throw out a few more options.

    i have seen where a guy ran his RO straight into a container and used a pump hooked to a DI canister and just ran the DI on the container in a closed loop theory. (it just continuously circulated and was able to remove the remaining stuff in the water.)

    on a second note, why not use one of your "Tee's" to connect both RO systems together and have them upgrade to a 3/8 line. then use one of your 300GPD canisters with DI in it. that way theres more contact time from size, but the 3/8 line and canister allows slower flow and might work out good (without having to change too much more)
  10. melev's Avatar
    Thanks for the suggestions. What I did today was run up to the LFS and get some DI resin to test his batch since it is from a different supplier.

    After running it for a few minutes:
    RO: TDS 13
    DI: 0 and PO4 measured .11

    So I pulled out the Salifert PO4 kit and measured the DI water.
    PO4 measured 0.

    Tested my 215g. PO4 measured 0.
    Tested the 400g. PO4 measured .03
    Tested the 250g. PO4 measured 0.

    Which calls into question the Hanna Checker's Phosphate Reagents. Either Salifert is right or the Hanna Checker is right. They can't both be right, that's for sure. I may need to update my product review.
  11. maroun.c's Avatar
    I'm guessing the Hanna Checker is wrong as the Salifert Reading is supported with the 0 TDS.
    Believe if you have phosphate in the water then your TDS can't be 0 as well.
  12. cyano's Avatar
    My elos kit would show zero phosphate yet I had a large HA problem, I did not realize until months in to the problem and after ordering the Hanna checker that my elos kit was expired. I wonder if due to the frequency you use your Hanna it may need a little internal cleaning?
  13. OneReef's Avatar
    What water pressure is going into your RODI unit from the source. I think mine is around 45 psi. Just wondering if faster or slower PSI would matter..... I guess it is similar to what you are talking about, just a different way to measure it maybe?
  14. Seth The Wine Guy's Avatar
    Dang Marc, I wish I saw this thread before you were here earlier this week. I would have had you up till 5am talking about it! I posted an almost identical thread/problem in my forum early this year without any answers. I was having PO4 issues and couldn't understand why given my filtration/equipment and WC schedule. I then tested water from my RODI with almost identical numbers as you did with my Hanna Bench top. (Not the pocket checker) If I remember correctly my RODI was testing around .07-.10. I questioned the checker and tested against someone else's Hanna bench top with identical numbers. Then, I took it to be tested against a very fancy photometer that can test for darn near everything. (I think it's around $2-3k) Same one the Georgia Aquarium uses. My Hanna was still dead on with a matching reading.
    I will rekindle my efforts to solve this issue. I didn't get much feedback from others because it seemed no one else ever tested their RO water. And, fwiw, I love Salifert test kits for everything BUT PO4 tests. I found it to be so far off it's laughable.
  15. melev's Avatar
    Well, I'd like to know what your final decision was. Your tank looks great, what is your current PO4 measurement? So the meter at the Georgia Aquarium also measured RO and RO/DI at higher than 0 readings?

    I've never doubted my Salifert test kits. Zero was clear liquid, any hint of blue was PO4. Depending on how blue it was, the worse the number.
  16. Seth The Wine Guy's Avatar
    Just to clarify, I meant that I tested my meter against the same photometer the GA Aquarium uses with the same water sample to see if they matched. I didn't care about testing my specific sample with their meter. I just wanted to see how both meters matched up with a control sample.<br><br>I haven't tested my premix SW in a very long time. I was resigned to the fact there was PO4 in it. Well, it just so happens I recently changed all the filters in my RODI except for the membrane. I tested my premix SW and it tested 0.00.&nbsp;<br><br>To answer your other question, I keep my PO4 between .03-.05. It's .05 right now. I do this by design because I find so much color is lost in my acros when I drop levels close to 0.00. I'm actually about to drop them lower for a while. I'm going to try increasing the "blue" lighting period time and shorten the 14k lighting time in an attempt to help with color. I run a MH/LED hybrid with 800w of MH and ~330w of LED. I run 6 on and 6 off. I'm cutting out the MH completely in one of the photo periods and using a 22k+ spectrum in it's place. It's more in depth than I'm going into here but too lazy to type ALL the details out.

    I'm going to keep checking my water periodically though. I'm very relieved to see a 0.00 flash up. I usually test twice if 0.00 shows. Did not do that today.