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Questions: UV, fertilizers, precipitation, and bioavailability?

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  • Questions: UV, fertilizers, precipitation, and bioavailability?

    I have been noticing that when I dose CSM+B, and sometimes K2SO4 my aquarium water looks a bit cloudy for a day. I'm wondering what's going on. I've been reading a few things here about iron and maybe some other stuff precipitating when exposed to UV and after catching something interesting while testing my aquarium water yesterday I'm really curious.

    I have a 70~80gal tank. I run a strong UV light for my system. 25w with flow throttled back to 2gpm to completely sterilize my water of even the toughest critters like viruses.

    After neglecting my plants for a month or so I've gotten back on the wagon with fertilizing and testing my water in prep for adding pressurized CO2 soon. The first time I tested my water everything was out of whack- high nitrates, high phosphates, almost zero iron, and although I have the reagents, I haven't calibrated my photospectrometer to test potassium levels yet but I think I'll be doing that shortly.

    So I dosed good & heavy with CSM+B and K2SO4 to get the nutrient levels balanced out, and then added as much Excel and Axis as I dared. The next day I tested the water again and got nearly zero iron again. This shouldn't be. I dosed for a target of .5ppm and I've never seen my plants take up that much iron in a day before. So this time I unplugged the UV light and dosed iron, excel and axis again. Only this time I noticed I didn't get the usual cloudy water and when I tested the water the next morning I had a solid iron residual. I plugged the UV back in and I'll test again later today to see if my suspicions are correct about the UV killing my iron levels.

    Which leads me to my questions:
    • Is this a known phenomenon, that UV causes Iron to precipitate?
    • When iron precipitates is it removed from the water column?
    • If it is removed from the water column, is it in the filter or the substrate?
    • If it is in the substrate, is it in a form bio-available to the plants?
    • Is there a better source of iron then CSM+B that is more stable under UV?
    • Does K2SO4 react the same way?

    Thanks in advance for taking the time.
    "Do, then talk about it.
    No do? No talk!!" - Tom Barr

  • #2
    Sterile Environment?

    tHi J,

    I think Anthony gave a good answer over at The Planted Tank.

    I guess I would say that consistent dosing is important. I do not consider dosing for .5-ppm iron with CSM+B to be particularly high.

    Why are surprised that the nutrients you toss in for the plants are not there later? The point of dosing is for the plants to consume.

    I question the need for such heavy use of UV-sterilization; I do not see the point. If our plants are to grow and our filters to work we do not want a sterile environment, we want a healthy living environment.

    The first sign we don't know what we are doing is an obsession with numbers. - Johann Wolfgang von Goethe

    Disclaimer: I am not trying to make you mad, it is just what I am, an evil plant monster, 'nuf said.
    • I believe the information I am giving is sound, I am not a veterinarian, professional chemist or particularly bright and certainly not a "Guru.".
    • I assume you are of legal age, competent and it is legal for you to acquire, possess and use any materials or perform any action in your in your jurisdiction.
    • When in doubt "don't."


    • #3
      My understanding of what an aquarium needs has been a long journey and perhaps this is just another step in the learning process for me. Several years ago my wife, then girlfriend and I set up our first aquarium and among other problems, lost some fish to disease due to not quarantining new additions. Not to mention bad green-water. UV put an end to both those problems. Now I'm trying to learn and take it to the next level with a planted tank. Sounds like I'll have to make some adjustments with my UV usage.

      My testing today more or less confirms my suspicions. The UV light is definitely stripping my water column of all the iron. I could keep testing to really eliminate all other variables but I'm convinced.
      Last edited by Oreo; 05-24-2010, 05:32 PM.
      "Do, then talk about it.
      No do? No talk!!" - Tom Barr


      • #4
        Updated the post above ^. I skipped a day of testing since Fe was already at zero and I hadn't dosed any the day before. Yesterday I turned the uv light off again and dosed heavy with iron. Low and behold, today there is a solid iron residual. I'm going to leave the UV light off for a few days without adding more Fe and track the "normal" drop in Fe concentration.
        "Do, then talk about it.
        No do? No talk!!" - Tom Barr


        • #5
          Please excuse my ignorance: spectrophotometers only measure Fe +2, or is it measuring any Fe in the water column (therefore measuring and isolating plant uptake)?

          Mind continuing NO3 and PO4 measurements alongside? The relative rate of each nutrient is interesting to me.

          Any chance you can use your tools to measure doses and drop off in containers with only water?

          Let's all grow great tanks.

          My plant tweets pics!


          • #6
            Well, I have to buy reagents for these tests so I try not to run tests unless I'm specifically looking for something. I've got a pretty good grasp of what my N & P are doing right now so I'll resume testing those in a few weeks when I get my pressurized CO2 system connected. I'll need to monitor things for a while to help get the system stabilized. (Also, when comparing my nutrient level changes keep in mind I run a constant tap water drip of about 7gal/day. The incoming tap water contains some PO4 but will displace some N, K, & Fe.)

            You're asking about testing "containers with only water", are you talking about like, a bottle of water or something? I could run a few tests on something like that if the community here thinks it would be helpful.

            The test I'm running measures total iron with an accuracy of +/- 0.01ppm (under ideal circumstances.) THIS PDF describes the test in detail but the summary of method reads as follows:
            "FerroVer Iron Reagent reacts with all soluble iron and most insoluble forms of iron in the sample, to produce soluble ferrous iron. This reacts with the 1,10 phenanthroline indicator in the reagent to form an orange color in proportion to the iron concentration."
            Last edited by Oreo; 05-22-2010, 02:21 AM.
            "Do, then talk about it.
            No do? No talk!!" - Tom Barr


            • #7
              Hey Oreo!

              Yes, I do mean a bottle of water. The reasoning is two fold, and I do believe it to be valuable to the community when sharing such data sets. You can use this to calculate input if you want it to save time and compare vs measured amounts, by the way: -- it does not care if you used, say, 0.050 L for a 50mL sample.

              a) We need a baseline for Fe reduction without the variables of plants and substrate's ability to get Fe. A baseline without inferring the data from your current sets.

              b) Down the line, you may be interested in testing different forms of chelated Fe, and if so, I can guarantee you a gratis source of at least two forms of chelated Fe (EDDHA and DTPA) for such tests.

              Good work and thanks.
              Let's all grow great tanks.


              My plant tweets pics!


              • #8
                Wet, lets talk about your proposed test in a little more detail. Would I be using deionized water or aquarium water? Would the bottle be stored in the dark or perhaps next to my aquarium to receive a comparable amount of light? Should it be refrigerated? How frequently & for how long would you like me to test? Every couple hours for a day? Or perhaps once a day for a few weeks? Are you specifically asking me to use only chelated iron or would CSM+B be sufficient? What should be the starting concentration?
                Last edited by Oreo; 05-25-2010, 01:47 AM.
                "Do, then talk about it.
                No do? No talk!!" - Tom Barr


                • #9
                  And since everyone always like pictures, here's a shot of my filtration setup. I figured it's relevant here by now.

                  There are two 1" PVC lines for the filter influent & effluent and a 1/2" line for the overflow-to-drain which makes the tap water drip possible. I have the overflow dripping into a nursery full of black molys and a goldfish at the moment which in turn overflows to a bucket I use for doing water changes in my hospital / quarantine tank (not in photo.) The influent line goes through two of my own custom designed heavy duty whole-house filter units run in parallel and then through one more unit with biomedia. From there the plumbing shrinks to 3/4" for the pump connections. After the pump the line splits with 4gpm going to the Hydor ETH 300w heater and 2gpm going to the Aqua 25w UV unit. From there the lines merge again and return to the aquarium. The tap water drip system runs through an under-sink carbon filter unit and then through a few cheap pressure regulators (to control the drip rate) and is injected into the aquarium system between the mechanical and bio-filters. The drip rate is monitored where the overflow stops above the nursery tank.

                  Last edited by Oreo; 05-24-2010, 06:30 PM.
                  "Do, then talk about it.
                  No do? No talk!!" - Tom Barr


                  • #10
                    My canister filter seems so inferior right now.


                    • #11
                      I did the canister thing. Decided I could do better. (I'm a municipal water treatment operator for crying out loud.) I've got a 3rd gen clarifier design in my head that I still need to build and add in too. It should allow me to remove most of the crud before it hits the filters and then I can remove the crud from the clarifier by just opening a valve & letting it drain. Been working on this system a long time. My goal is to have it perfected by the time I get around to setting up a 1,000gal aquarium.

                      That, and I got really, really friggin tired of leaky tubing junctions after I lost about 50gal all over my brand new hard wood floors that I busted my own arse installing. It was then I decided to throw caution to the wind and plumb the whole thing with rigid PVC into the basement. That was the best decision ever.

                      Also, I've been updating this chart below.

                      For the record:

                      I use a Hach DR2000 spectrophotometer for all my water tests. It's pretty dang accurate / not your usual aquarium test kit.

                      5/15/2010 - (Dosed lots of NO3, a little PO4 & K, and very little Fe. UV light is ON.)
                      5/16/2010 - NO3 = 33.1ppm --- PO4 = 6.30ppm --- Fe = 0.02ppm (After testing I dosed to .5ppm iron, lots of Excel & Axis for carbon. UV light is ON.)
                      5/17/2010 - NO3 = 28.3ppm --- PO4 = 6.00ppm --- Fe = 0.01ppm (After testing I dosed to 1.0ppm iron, 1.0ppm K, lots of Excel & Axis. Turned UV light OFF.)
                      5/18/2010 - NO3 = 24.4ppm --- PO4 = 5.88ppm --- Fe = 0.82ppm (After testing I dosed Excel & Axis. Turned UV light back ON)
                      5/19/2010 - NO3 = 23.1ppm --- PO4 = 4.64ppm --- Fe = 0.03ppm
                      5/20/2010 - ------------------------------------------------------ (No testing done today. Dosed lots of CSM+B, turned UV light OFF)
                      5/21/2010 - ------------------------------------- Fe = 1.56ppm
                      5/22/2010 - ------------------------------------- Fe = 1.46ppm
                      5/23/2010 - ------------------------------------- Fe = 1.37ppm (I'm noticing an interesting trend here. About .1ppm reduction in iron residual per day.)
                      5/24/2010 - (12:30 pm) -------------------------- Fe = 1.23ppm (UV light turned ON after test. yesterday evening I fed a very small amount of CO2 directly into the filter intake as an equipment trial.)
                      5/24/2010 - (01:00 pm) -------------------------- Fe = 1.20ppm
                      5/24/2010 - (01:30 pm) -------------------------- Fe = 1.09ppm
                      5/24/2010 - (02:30 pm) -------------------------- Fe = 0.92ppm
                      5/24/2010 - (03:30 pm) -------------------------- Fe = 0.78ppm (Running some quick calculations, I predict Fe residual to have been completely removed by about 9pm this evening.)
                      5/24/2010 - (08:00 pm) -------------------------- Fe = 0.39ppm

                      Anyone still not convinced the UV light is removing my iron residual?
                      Last edited by Oreo; 05-25-2010, 01:55 AM.
                      "Do, then talk about it.
                      No do? No talk!!" - Tom Barr


                      • #12
                        Hey, Oreo. I am sorry for missing this!

                        I think you should use DI water if possible, but even if there do happen to be bacteria and other critters free floating, that this doesn't matter too much (for the same reason as the next thing).

                        I think you should not care about light or refrigeration because, well, we know our tanks have light and I am more interested in the practical/applied numbers.

                        I think once a day testing is fine but throughout the day, if you have time, is even better!

                        I think CSM+B is fine for these baselines with and without UV. But I am offering you some stuff to play with if you are interested, too, or don't mind running some samples for fellow nerds. (The impetus for that idea was the threads and active discussion a few months ago on different forms of Fe -- happy to search and link if you'd like and may help brainstorm.)

                        I think the same as your typical tank input is fine since your equipment appears so accurate we don't need to round up or anything.

                        I can completely understand doing more samples than this request or changing methodology. The original request was simply for a control outside your tank <3

                        Plumbing pics are always cool. Thank you for sharing it!
                        Last edited by Wet; 06-02-2010, 01:39 AM.
                        Let's all grow great tanks.


                        My plant tweets pics!


                        • #13
                          OK, DI water makes sense and for the most part I agree that bacterial contamination is probably not a major concern. As far as light & temp it sounds like a transparent bottle sitting next to my aquarium would give the most practical results. Clearly, UV exposure is out of the question. For initial Fe residual you're thinking about 1ppm then? That sounds fine. Unless there is already some evidence that chelated Fe will decompose at a rate detectable from hour to hour then I suggest testing perhaps once a day or every other day for a week or so. To me that begs the question though... do we have some reason to suspect the chelated iron residual in an aquarium environment is decomposing at a significant rate? (Did I miss that thread?)
                          "Do, then talk about it.
                          No do? No talk!!" - Tom Barr


                          • #14
                            Very good thread. I seemed to have missed it before. Having the same issue here. UV on = no measureable Fe. UV off =no problem.

                            Last edited by dutchy; 03-15-2011, 09:51 PM.

                            My 2011, 2012 and 2013 AGA aquascaping contest entries:


                            • #15
                              I have just noticed this in my tank. Is there anything we can do besides leaving the UV light off? My plants seem to be fine (no yellowing) with the lack of iron showing in the tank. Is there anything elese that I can look for that shows lack of iron?