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Old 03/05/2018, 04:23 PM   #1
Dan_P
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Skimmer PO4 Removal Study

Here is a quick summary of data I collected on the phosphate content in skimmate produced in my DIY skimmer. I plotted the % of the systemís phosphate removed per hour against the volume of skimmate as a percent of the total volume of the system produced per hour. To clarify, a bit less than 2% of the systemís phosphate is removed per hour when the amount of collapsed foam produced per hour is 0.1% of the systemís total. My system is about 187 liters and PO4 level during the study was around 0.01 ppm. For aquarists doing daily 1% water changes by wet skimming are potentially removing a significant amount of phosphate.




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Old 03/05/2018, 07:07 PM   #2
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How are you measuring phosphate? Is this data from a total phosphate kit, or a standard orthophosphate test?


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Old 03/06/2018, 05:35 AM   #3
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How are you measuring phosphate? Is this data from a total phosphate kit, or a standard orthophosphate test?
Hanna low range orthophosphate.

Here is an interesting observation. Holding the foamate solution at pH 3 for five minutes before neutralizing the solution and centrifugation (to clarify the foamate sample) increases the phosphate level. Ken Feldman thinks it might be a result of dissolving something inorganic like an insoluble salt or carbonate shell rather than hydrolysis of phosphate esters.

The results are definitely a head scratcher given the way skimmers work. I donít know what is actually being collected by the foam. Besides arsenic, I have not found any information on substances that would produce false positives. Still looking and listening though. I am tempted to purchase the Hach total phosphate kit.


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Old 03/06/2018, 08:13 PM   #4
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Fairly obviously, I am not sure why there's so much phosphate in the skimmate, either. Maybe there's enough decay happening, but that seems odd. I don't have enough chemistry background to comment on what the acid might be doing. I would have thought it was breaking down at least some organics, but maybe not.


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Old 03/06/2018, 08:26 PM   #5
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Used to perform environmental sampling all the time and we had to acidity sample to pH<2 with nitric acid. Not sure exactly why though. Maybe prevents conversion to orthophosphate? Maybe Randy can chime in?


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Old 03/07/2018, 04:09 AM   #6
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The skimmer is taking in bacteria they die= release of phosphate

Skimmer takes in particles of food,waste, ect.......it breaks down= phosphate

These are just my guesstimations of what happens

I don't think anyone knows what is actually taken up at the point of reaction/frationation........it's all supposition and theory based on what the test numbers read. I know there is an article or two about bacteria counts but I think the value and conclusions are overstated in relation to how to run a reef tank.

I'm curious why are you focusing on such minutiae? Other than for interest and conversation I don't see the value.

Just for fun you should test the water before it goes to the skimmer and the water after........maybe that will give you more answers or more questions


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Old 03/07/2018, 04:48 AM   #7
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Originally Posted by bertoni View Post
Fairly obviously, I am not sure why there's so much phosphate in the skimmate, either. Maybe there's enough decay happening, but that seems odd. I don't have enough chemistry background to comment on what the acid might be doing. I would have thought it was breaking down at least some organics, but maybe not.
I looked into the notion of decomposition by collecting samples and analyzing them immediately, some even after cleaning the skimmer. No apparent effect. Even before this experiment, I let skimmate sit at room temperature in a capped vial. Little changed over several days. None of this is solid proof but it is suggestive that decomposition may not be an important factor.

As for breaking down organics, in this case hydrolysis of phosphate esters, it requires strong acid and high temperatures. This is not a rejection of breaking down organics idea, just saying that there is something more to investigate.


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Old 03/07/2018, 04:52 AM   #8
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Used to perform environmental sampling all the time and we had to acidity sample to pH<2 with nitric acid. Not sure exactly why though. Maybe prevents conversion to orthophosphate? Maybe Randy can chime in?
Do you remember what the subsequent tests were? The use of nitric acid would dissolve carbonates and phosphate salts but allow you to analyze for chloride and sulfate.


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Old 03/07/2018, 05:55 AM   #9
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The skimmer is taking in bacteria they die= release of phosphate

Skimmer takes in particles of food,waste, ect.......it breaks down= phosphate

These are just my guesstimations of what happens

I don't think anyone knows what is actually taken up at the point of reaction/frationation........it's all supposition and theory based on what the test numbers read. I know there is an article or two about bacteria counts but I think the value and conclusions are overstated in relation to how to run a reef tank.

I'm curious why are you focusing on such minutiae? Other than for interest and conversation I don't see the value.

Just for fun you should test the water before it goes to the skimmer and the water after........maybe that will give you more answers or more questions
It certainly does look like I am counting angels on the head of a pin :-) Wait until you see my survey on the number of dinoflagellates collected per mL of skimmate!

I am uneasy about depending on water purification methods like a skimmer or GAC column that are currently impossible for us to assess how well they are performing. Relying on manufacturers recommendations does not necessarily help me. Since there is no transparency in how they came up with their recommendations, I cannot judge if a manufacturer's recommendations are relevant. Ken Feldman published a lot of information on skimmers in Advanced Aquarists, but even that amount of knowledge did little to convince me that I knew how well my skimmer were working. Hence, the study.

Where the phosphate is coming from is a tough question to answer but skimmate collected over an hour and then immediately analyzed for phosphate shows a phosphate concentration much higher (20-100 X) than that of the aquarium water. Typically, my system has a 0 - 0.03 ppm phosphate level. This observation suggests, not proof, that something is being collected by the foam rather than bacterial metabolism or decay in the skimmate producing phosphate.

As for comparing aquarium water to skimmer effluent, very little material is collected per second by a skimmer. The difference is undetectable and only over time does the skimmer remove measurable amounts of material. In skimmer theory jargon, the "recovery rate" for a skimmer attached to an aquarium is very low.


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Old 03/07/2018, 12:53 PM   #10
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It could be interesting to test the skimmer in a static environment like a bucket with a known volume and phosphate level and then check the phosphate level in the water over time. That would give you a measurable removal rate. You could also measure skimmate production and see how that relates to the phosphate level as it declines.

There would be some loss in efficiency as the phosphate level is reduced but at least you'd have some removal rates at various phosphate levels without having to measure the skimmate.

.1% per hour sure seems like a lot of skimmate. Do many people run systems that wet?


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Old 03/07/2018, 04:59 PM   #11
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It could be interesting to test the skimmer in a static environment like a bucket with a known volume and phosphate level and then check the phosphate level in the water over time.
Like it.

I did something like this with a GAC column. May try it with a skimmer.

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.1% per hour sure seems like a lot of skimmate. Do many people run systems that wet?
I donít know the answer to the preferences but wetter skimate results in removing more material per hour. Unless water conservation is an important factor or time to empty the collection bucket is limited, it seems like skimmers should be run as wet as practical. 0.1% for my 187 liter would be about 200 mL an hour or 4.8 liters a day. On the other hand people do 1% per day water changes which for my system would be about 2 liters per day. I typically try to keep the skimmer air flow adjusted to produce about 2 liters per day. The amount of scum collecting on the skimmer walls seems much reduced.


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Old 03/07/2018, 06:22 PM   #12
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I donít know the answer to the preferences but wetter skimate results in removing more material per hour. Unless water conservation is an important factor or time to empty the collection bucket is limited, it seems like skimmers should be run as wet as practical. 0.1% for my 187 liter would be about 200 mL an hour or 4.8 liters a day. On the other hand people do 1% per day water changes which for my system would be about 2 liters per day. I typically try to keep the skimmer air flow adjusted to produce about 2 liters per day. The amount of scum collecting on the skimmer walls seems much reduced.
So your ATO would be a salt mix?


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Old 03/07/2018, 06:49 PM   #13
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So your ATO would be a salt mix?
I havenít automated this. I replace the skimmate volume with new salt water twice a day when I measure the skimmate volume at 6 AM and 5 PM. After the salt water is replaced, I evaluate fresh water replacement need, which is about a gallon per day in the winter. I am not sure how you would automate both types of water replacements.


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Old 03/07/2018, 11:18 PM   #14
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I havenít automated this. I replace the skimmate volume with new salt water twice a day when I measure the skimmate volume at 6 AM and 5 PM. After the salt water is replaced, I evaluate fresh water replacement need, which is about a gallon per day in the winter. I am not sure how you would automate both types of water replacements.
I suppose you could figure how much evaporation is average and just dilute the salt make up. I couldn't run this wet without some automation as I travel for a living.


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Old 03/08/2018, 12:25 AM   #15
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I love your study. Not being a chemist/biologist/scientist, I can’t comment on your studies validity. But I think it is fantastic that a hobbyist is injecting some quantifiable science into our shared passion. Far too much of the information in our hobby is based on anecdotal evidence, which is the weakest form of knowledge. Thumbs up!!!


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Old 03/08/2018, 01:29 AM   #16
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I love your study.
Thank you.


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Old 03/09/2018, 07:53 AM   #17
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Hanna low range orthophosphate.

Here is an interesting observation. Holding the foamate solution at pH 3 for five minutes before neutralizing the solution and centrifugation (to clarify the foamate sample) increases the phosphate level. Ken Feldman thinks it might be a result of dissolving something inorganic like an insoluble salt or carbonate shell rather than hydrolysis of phosphate esters.

The results are definitely a head scratcher given the way skimmers work. I donít know what is actually being collected by the foam. Besides arsenic, I have not found any information on substances that would produce false positives. Still looking and listening though. I am tempted to purchase the Hach total phosphate kit.
Hi Dan!
Was just reading through your post, interesting find
Just a heads up on someone who uses hach equipment daily. Our business has just about every colorimiter they make. Imo they are awesome and worth ever penny since we have some of the old series 1 units still in use after 20 years of beeing dragged all over creation.
If you decide to take the plunge I'd highly recommend the DR900 for the price difference as there are many many more uses.
The other brand we use regularly is lamontte these have also been is use for 20+ years (we have of 1200 series) and their worth their weight in gold
We always keep two of any type test to verify results and use these two brands interchangeable and to verify each other.
As a side note I don't work for or receive any compensation from hach or lamontte I've just used their products and find them reliable.

Sometimes you can find either of these kits on places like eBay for a good deal if your up for a gamble btw.
Good luck!! Keep looking for those answers!

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Old 03/09/2018, 10:35 AM   #18
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If you decide to take the plunge I'd highly recommend the DR900 for the price difference as there are many many more uses.
Thanks for the recommendation. I have seen this model on the Hach web site. It would be an amazing piece of equipment to own.


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Old 03/09/2018, 11:12 AM   #19
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Thanks for the recommendation. I have seen this model on the Hach web site. It would be an amazing piece of equipment to own.
They are pretty sweet.. on a normal basis I do use red Sea kits but if there's any question i "borrow" one of our work kits (it's a whole 20' walk to the office lol) for things like po4 and phosphorus there's no beating it. For business we do free and total cl2, no2, no3, nh3/4, turbidity, do, temp, pH, Fe, mn, pb, and cu daily and it's very nice to use just one piece of equipment. I haven't gone through every test with salt water but also haven't had any issues where I noticed that it didn't work with saltwater on parameters I normally test.

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