Dwell Time for Protein Skimmers?
- Thread starter keithhays
- Start date
reefgeezer
Active member
For non-recirculating skimmers: Calculate the volume of the skimmer's body in cubic inches divided by 231. This yields the volume of the skimmer body in gallons. Divide the pump's flow (in GPH) by 3600 to get gallons per second. Divide the skimmer's volume by the flow in gallons per second. That will yield the dwell time in seconds... I think. So...
My skimmer body is 6" ID and 20" tall. 3 X 3 = 9 then 9 X 3.1416 = 28.3 then X 20 = 566 Cu In. Then divided by 231 = 2.5 gallons in round numbers. My pump pumps 700 GPH so: 700 divided by 3600 = .2 gallons per second. Then 2.5 divided by .2 = 12.5 seconds dwell time... I think.
My skimmer body is 6" ID and 20" tall. 3 X 3 = 9 then 9 X 3.1416 = 28.3 then X 20 = 566 Cu In. Then divided by 231 = 2.5 gallons in round numbers. My pump pumps 700 GPH so: 700 divided by 3600 = .2 gallons per second. Then 2.5 divided by .2 = 12.5 seconds dwell time... I think.
Awesome. Thank you..now the I have to go figure out what the volume of an aquac 400 is and how much water is actually coming out of it. I have been looking everywhere. You would think given how much money we spend on these things that it would be labeled on all of them..
reefgeezer
Active member
If it has a box on the bottom and a tube on top figure the volume of each and add them together. Be sure to account for all the plumbing inside the box. I'd use 90% of the box's volume plus the tube's volume. The box volume in gallons can be calculated by multiplying length X width X height and dividing by 231.
So on the AQUAC EV400
The base is 832.8125 cubic inches
The riser is 353.565 cubic inches
or 1186.3775 cubic inches
or 5.14 gallons
The iwaki MD55RLT is below the unit by 2 feet and the unit puts significant back pressure on it and it flows all its water through a 1-1/2" pvc with little capacity left over, so I am going to guesstimate 1000 gph divided by 3600 = .28 rounded
5.14 divided by .28 = 18.3 seconds rounded dwell time
I suspect the actual water flow is a little lower, but until I get bucket under it, I won't know for certain.
Yeh! now I have a way to compare skimmers.
The base is 832.8125 cubic inches
The riser is 353.565 cubic inches
or 1186.3775 cubic inches
or 5.14 gallons
The iwaki MD55RLT is below the unit by 2 feet and the unit puts significant back pressure on it and it flows all its water through a 1-1/2" pvc with little capacity left over, so I am going to guesstimate 1000 gph divided by 3600 = .28 rounded
5.14 divided by .28 = 18.3 seconds rounded dwell time
I suspect the actual water flow is a little lower, but until I get bucket under it, I won't know for certain.
Yeh! now I have a way to compare skimmers.
Neogenocide
New member
How would you figure a recirculating skimmer? It's a question I've had sticking in the back of my mind for quite a while now.
I am not sure if the calculation is different, but you could check it out on these industrial recirculating models which publish the sizes, gpm, dwell time, etc. If nothing else you could scale down the size and rate.
http://www.emperoraquatics.com/proteinskimmer.php
just remember these guys are GPM and not GPH, when you do the calculation.
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On the 46"x170" RECIRCULATING model they have listed 1.5min dwell time @ 570 GPM
If you use the same calculation:
It is 282632 cubic inches or 1223.5 Gallons
Since we already in GPM it is 570 GPM
1223.5 divided by 570 = 2.15 minutes dwell time
It could be that the vendor is being conservative to be certain of at least 1.5 minutes of dwell time (more likely as it would also cause up selling to the next model) or they are doing some calculation to account for the same water moving back through the main chamber or for bubble destruction and reconstruction.
addition: I think I know what it is: the dimensions for the skimmers include the entire unit including the waste collection tower. I don't see the exact dimensions of the base so it looks like the calculation should be right on target if you subtract a 1/4 of the height or so. i.e. re circulation doesn't appear to affect dwell time per an individual molecule of water. I suspect the usefulness of re circulation is in the multiple passes to strip out items that did get pulled the first time. I actually have my non-recirculating skimmer setup in a configuration with two sumps so that 1/3 of the water coming back from the skimmer sump is mixed with 2/3 of water falling from the tanks to achieve the same thing.
If you use the same calculation:
It is 282632 cubic inches or 1223.5 Gallons
Since we already in GPM it is 570 GPM
1223.5 divided by 570 = 2.15 minutes dwell time
It could be that the vendor is being conservative to be certain of at least 1.5 minutes of dwell time (more likely as it would also cause up selling to the next model) or they are doing some calculation to account for the same water moving back through the main chamber or for bubble destruction and reconstruction.
addition: I think I know what it is: the dimensions for the skimmers include the entire unit including the waste collection tower. I don't see the exact dimensions of the base so it looks like the calculation should be right on target if you subtract a 1/4 of the height or so. i.e. re circulation doesn't appear to affect dwell time per an individual molecule of water. I suspect the usefulness of re circulation is in the multiple passes to strip out items that did get pulled the first time. I actually have my non-recirculating skimmer setup in a configuration with two sumps so that 1/3 of the water coming back from the skimmer sump is mixed with 2/3 of water falling from the tanks to achieve the same thing.
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Several years ago I read an article about skimmers (no clue when or from where) and the author discussed dwell time in terms of minutes, between 5 – 10, before there was enough contact time for some of the wastes to attach to the air bubbles.
Anyone else recall something similar? I am probably way off because this was when I was building my 4 ft. skimmer that sat outside the stand that my wife just loved with a passion.
Anyone else recall something similar? I am probably way off because this was when I was building my 4 ft. skimmer that sat outside the stand that my wife just loved with a passion.
Most industrial skimmers will give measurements in terms of minutes and GPM instead of GPH. Minimally, what I have seen so far on their sites is 1.5 minutes dwell time at 11 gpm I don't know this particular article, but I have seen measures where for instance in order to sterilize water with ozone you need at least 4 minutes..and an air chamber to degass it.
Also, I have seen some where there are some substances that will only skim out at X number of minutes.
Updated AQUAC 400 DWELL TIME
Updated AQUAC 400 DWELL TIME
So on the AQUAC EV400
The base is 832.8125 cubic inches
The riser is 353.565 cubic inches
or 1186.3775 cubic inches
or 5.14 gallons
Using the iwaki MD55RLT with 2 ft head
The actual flow rate is slightly over 700 GPH.
700 GPH divided by 3600 = .194 gallons per second
5.14 divided by .194 = 26.49 seconds rounded dwell time
26.49 seconds dwell @ 11.66 GPM
Updated AQUAC 400 DWELL TIME
So on the AQUAC EV400
The base is 832.8125 cubic inches
The riser is 353.565 cubic inches
or 1186.3775 cubic inches
or 5.14 gallons
Using the iwaki MD55RLT with 2 ft head
The actual flow rate is slightly over 700 GPH.
700 GPH divided by 3600 = .194 gallons per second
5.14 divided by .194 = 26.49 seconds rounded dwell time
26.49 seconds dwell @ 11.66 GPM
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The AQUAC EV 400 is rated for systems between 150 to 400 gallons
and will process the following for 26.49 seconds of dwell @ 11.66 GPM :
I used the following calculator with the following parameters:
Water Change Volume = 11.66 U.S. GALLONS
Water Change Every = 1 minutes
Calculate Effective Water Change After: was increase incrementally until any number above 99% was reached
http://www.hamzasreef.com/Contents/Calculators/EffectiveWaterChange.php
and will process the following for 26.49 seconds of dwell @ 11.66 GPM :
- 99.22% of 150 gallons in 1 hour
- 99.14% of 300 gallons in 2 hours
- 99.65% of 400 gallons in 4 hours
I used the following calculator with the following parameters:
Water Change Volume = 11.66 U.S. GALLONS
Water Change Every = 1 minutes
Calculate Effective Water Change After: was increase incrementally until any number above 99% was reached
http://www.hamzasreef.com/Contents/Calculators/EffectiveWaterChange.php
Neogenocide
New member
I'll have to measure my skimmer tonight and figure out the volume. It's a Geo, 8" body, don't remember the height though. Has a Sedra 9000 pump on it.
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