Whats the best way to determine DOC (dissolved organic compounds)?

[chaostactics]

TLR My skimmer is doing nothing*; is my tank "too clean"? I have a system with approximately 90 gallons total volume. Current bioload is a royal gramma, 2 clown, and a shark nose goby (plus a bunch of zoa). I feed the fish once a day, feed 1/8 reef roids a few days a week, and a couple of tiny silversides to my anemones a couple of times a week.

I have dual filter socks that I change every 3 days or so, a SKIMZ MBR-157 algae reactor, a carbon reactor running 9 Tbsp ROX, and an older Bubble Magnus 5.5 skimmer and the tank gets a 10% water change every 3 weeks. The skimmer seems halfway decent, however, when I have it tuned as far as it will go without flooding the skimmer cup it *barely pulls any skimmate.

So how do I figure out if there's just not enough DOC for the skimmer to create surface tension to create adequate foam or is it that the skimmer just sucks? [The skimmer has been cleaned and has been given time to break in, the skimmer chamber is at a constant and manufacturer recommended depth, and the water level inside the skimmer cannot be raised any higher without flooding the skimmer.

 

[Reefer5640]

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[Sallstrom]

DOC is usually dissolved organic carbon and that can be tested at Triton lab.

Dissolved organic carbon - Wikipedia

en.wikipedia.org

N-DOC

The most experienced in solution based water chemistry in the industry. Continuing to revolutionise reef keeping worldwide since 2008.

www.triton-lab.de

 

[chaostactics]

DOC is usually dissolved organic carbon and that can be tested at Triton lab.

Dissolved organic carbon - Wikipedia

en.wikipedia.org

N-DOC

The most experienced in solution based water chemistry in the industry. Continuing to revolutionise reef keeping worldwide since 2008.

www.triton-lab.de

For some reason I thought i rememberd the DOC in tunze DOC standing for dissolved organic compound. Thats where I got DOC from.

 

[Scrubber_steve]

For some reason I thought i rememberd the DOC in tunze DOC standing for dissolved organic compound. Thats where I got DOC from.

Compound - Carbon,,, same thing. Sometimes DOC is referred to as disolved organic matter.

 

[Scrubber_steve]

With your low fish stock & multifaceted array of filtration aparatus I wouldn't expect much action from your skimmer, particularly when using ROX

 

[Randy Holmes-Farley]

Just keep in mind that not all doc is skimmable. I’m not sure how one would use a single DOC number to know if a skimmer is working or not. If you had numbers from when using the skimmer and not using it, thst could be interesting, but there’s no rule of thumb how much it should decline.

 

[Dana Riddle]

DOC usually refers to Dissolved Organic Carbon. This can loosely be determined through the Biochemical Oxygen Demand test (and I have, always below 1 mg/l. Treated wastewater effluents are usually allowed up to 30 mg/l.) If you're employing a decent skimmer and regular water changes, I wouldn't be concerned about excessive organic carbon.

 

[Backreefing]

Back to the skimmer. If you determine it is working correctly, and still it pulls insignificant amounts of waist out . Then just take it offline after all what’s it doing besides making noise and useing electricity.

 

[Jase4224]

BRS did a video recently that had a simple test for water cleanliness..
1. Prepare a bucket of properly mixed salt water.
2. Syphon the same volume bucket of tank water and compare the colour of the two.

Use white buckets, and make sure that you have not stirred up the tank water or just fed the tank before syphoning. If the tank water clarity is close to the freshly mixed salt water then that is a good indication that your tank is clean. If your tank water is yellow then you need to improve either filtration method or maintenance.

 

[ReefGeezer]

You don't have much in the way of bioload in the tank yet so the skimmer might not kick out too much. As someone else said, skimmers only get a portion of the available organic load. ROX gets a different portion of it also. Be patient. If you must, you can always turn off the skimmer for part of the day and reduce the amount of ROX, but I'd do so in small increments. However, if your Zoas are happy, i would worry about it.

 

[taricha]

This can loosely be determined through the Biochemical Oxygen Demand test (and I have, always below 1 mg/l.

What was the time? Was that a standard 5 day BOD test?

@Dan_P and I also have done some BOD tests. A dissolved oxygen meter or O2 test kit is needed. Totally doable for a hobbyist.
Dan's also used a Chemical Oxygen Demand test (see thread for example - What's in your substrate?)

The yellow-ness of water is also caused by stuff that overlaps with DOC called Chromophoric Dissolved Organic Material (CDOM). A standard method to estimate DOC using this is to measure the water absorbance at 254nm. This is hard to do for hobbyists. But the bucket test mentioned above gets at the same thing.

A fun one to play with is fluorescent dissolved organic material FDOM. Some of the materials that cause yellowness in our tank water also fluoresce blue-green in response to UV light.

This extreme example was some tank water that I put in a beaker for a couple of days with a tiny pinch of fish flake. You can see the distilled water above it puts off no light, but the glass cuvette of sample water glows bright blue-green. (I actually had to decrease the sensitivity to measure it on my spectrometer.)

You can use a cheap little $10-20 UV flashlight like this one I got.


365nm seems to work best. Tank water gives a faint greenish glow.

But triton NDOC is the only service I know of that can actually calculate DOC numbers - literally how much carbon there is.

 

[Dana Riddle]

What was the time? Was that a standard 5 day BOD test?

@Dan_P and I also have done some BOD tests. A dissolved oxygen meter or O2 test kit is needed. Totally doable for a hobbyist.
Dan's also used a Chemical Oxygen Demand test (see thread for example - What's in your substrate?)

The yellow-ness of water is also caused by stuff that overlaps with DOC called Chromophoric Dissolved Organic Material (CDOM). A standard method to estimate DOC using this is to measure the water absorbance at 254nm. This is hard to do for hobbyists. But the bucket test mentioned above gets at the same thing.

A fun one to play with is fluorescent dissolved organic material FDOM. Some of the materials that cause yellowness in our tank water also fluoresce blue-green in response to UV light.

This extreme example was some tank water that I put in a beaker for a couple of days with a tiny pinch of fish flake. You can see the distilled water above it puts of no light, but the glass cuvette glows bright blue-green. (I actually had to decrease the sensitivity to measure it on my spectrometer.)

You can use a cheap little $10-20 UV flashlight like this one I got.


365nm seems to work best. Tank water gives a faint greenish glow.


But triton NDOC is the only service I know of that can actually calculate DOC numbers - literally how much carbon there is.

Yes, 5-day incubation at 20C in darkness. I use a Hach LDO (luminescent dissolved oxygen) probe and HQ40d meter. Reads DO to 1/100th mg/L.
Question about the COD. I used the dichromate reflux method, but some element in seawater interferes and I could never generate a usable number. Hach has two newer methods (one containing mercury) - I haven't tried either of them for seawater.

 

[LC8Sumi]

I wonder how much DOC fresh filter floss has, cause my skimmer loves to skimm that)PP (I hope you understand what I’m trying to point out)

 

[W1ngz]

I'd look at it from a far simpler approach, your nitrates and phosphates would come from dissolved organics just as well as any organic carbon would. If your nitrate and phosphate are low, and stay low, then your light bioload is already balanced by other means and the skimmer is just extra.

 

[Dana Riddle]

Yes, 5-day incubation at 20C in darkness. I use a Hach LDO (luminescent dissolved oxygen) probe and HQ40d meter. Reads DO to 1/100th mg/L.
Question about the COD. I used the dichromate reflux method, but some element in seawater interferes and I could never generate a usable number. Hach has two newer methods (one containing mercury) - I haven't tried either of them for seawater.

Forgot to mention - the BODs weren't dosed with a nitrification inhibitor, so they were carbonaceous plus nitrogenous oxygen demand. I've got to get into the lab and get serious about testing - I'm just now regaining strength after that nasty bout with the flu.

 

[Dan_P]

TLR My skimmer is doing nothing*; is my tank "too clean"? I have a system with approximately 90 gallons total volume. Current bioload is a royal gramma, 2 clown, and a shark nose goby (plus a bunch of zoa). I feed the fish once a day, feed 1/8 reef roids a few days a week, and a couple of tiny silversides to my anemones a couple of times a week.

I have dual filter socks that I change every 3 days or so, a SKIMZ MBR-157 algae reactor, a carbon reactor running 9 Tbsp ROX, and an older Bubble Magnus 5.5 skimmer and the tank gets a 10% water change every 3 weeks. The skimmer seems halfway decent, however, when I have it tuned as far as it will go without flooding the skimmer cup it *barely pulls any skimmate.

So how do I figure out if there's just not enough DOC for the skimmer to create surface tension to create adequate foam or is it that the skimmer just sucks? [The skimmer has been cleaned and has been given time to break in, the skimmer chamber is at a constant and manufacturer recommended depth, and the water level inside the skimmer cannot be raised any higher without flooding the skimmer.

You received very good responses to your question.

Are you absolutely sure that the skimmer throat or riser surface is free of bubble destroying compounds? It seems that during the manufacture of plastic items, the surface seems to pick up something that can weaken bubbles. I assume it is a mold release. It takes washing or use to rid the surface of the stuff. Skimming should start up quickly but might take an hour or more to stabilize at the clean surface builds up a film.

Skimmate formation requires a very small amount of organic matter to adhere to and strengthen air bubbles so that they survive the journey to the top of the skimmer throat. The strengthening depends both on the type of organic compound in the system and the amount. Not all organic matter strengthens air bubbles to the same degree. Some organic matter, like the oils from silversides you feed your anemones, can completely collapse the foam in the skimmer throat. Water changes can shut down foam formation for a time presumably through the dilution of the organic compounds. As for the effect of ROX, I I use 2 liters of Marineland GAC for a 100 gallon system and have never seen a fresh charge of GAC upset skimmate production. So, for now let’s assume the 9 Tbsp of ROX is not a factor.

Using the level of dissolved organic carbon (DOC) as a diagnostic for skimmer performance might work, though I don’t know whether anyone has done that. There are plenty studies of skimmer performance versus the concentration of protein or a specific compound. Because DOC represents all organic carbon and not just the type that strengthens air bubbles, the measure might not be useful to you.

Another thing to check into is your notion of “good” skimmer performance. What does good look like? Your perspective might be misleading you. For example, how many liters of skimmate per day is good? Most skimmer operators think a small amount of black skimmate and a collection cup with thick crud is a sign of peak performance. This is like thinking a sputtering and smoking car is a sign of good performance.

A side note. Ever wonder why skimmer manufacturers never, ever publish performance data for their skimmers?

Finally, I imagine your skimmer is working fine. The amount of organic material that makes skimmer insides look crudy is low. The manufacturer’s settings are probably incorrect for the conditions in your system.

 

[Dan_P]

I wonder how much DOC fresh filter floss has, cause my skimmer loves to skimm that)PP (I hope you understand what I’m trying to point out)

The filter floss is contaminated with a surfactant I would guess. I rinse my floss in a bucket if hot water to remove it. No skimmer out of control now.

 

[Dan_P]

Yes, 5-day incubation at 20C in darkness. I use a Hach LDO (luminescent dissolved oxygen) probe and HQ40d meter. Reads DO to 1/100th mg/L.
Question about the COD. I used the dichromate reflux method, but some element in seawater interferes and I could never generate a usable number. Hach has two newer methods (one containing mercury) - I haven't tried either of them for seawater.

Chloride is the interfering species because it is oxidized to chlorine. No way around it.

I seem to recall that mercury is used to precipitate chloride, though I don’t know whether that is practical for a seawater sample.

I am looking into basic KMnO4 oxidation for DOC estimations. Even though KMnO4 has fallen out favor for not oxidizing organics as thoroughly as chromate and persulfate, I figure it might be worth a shot to see if it would at least allow me to trend DOC as oppose to giving me an absolute number. As my first attempt at “validating” the method, I ran a series of skimmate dilutions in tank water (my tank water water seems to have a low COD. I still need to compare COD to N-DOC TOC) and got a ruler straight line of KMnO4 consumed vs skimmate concentration, though not happy with zero point. So, this N of 1 test looks very good but I need to understand the zero point shift. I will report back on this topic.

 

[taricha]

Other than skimming, UV light and ozone also reduce the yellow-ness of water, but I wonder if the oxidation and UV only modify the structure of the organic molecules that absorb light, OR do they actually change the availability of dissolved organic material for organisms to consume.
In other words, do they make the water cleaner (lower in organic nutrients) or just clearer (less yellow)?