Who rates skimmers

[robert]

Brad - yes, re-circ'd is what I have done to G5. You have PM
Cheers.

Originally Posted by untamed

Yup, that is the math...If the chamber size is constant, then increasing flow rate (tank turnover) reduces dwell time and vice-versa. Assuming that you have re-circ'd the G5, then you can control the flow rate. If you haven't re-circ'd, then your flow rate is set by the amount of water drawn in by the NW pumps and you would have no control over it.

Really, controlling flow rate is one of the big reasons why one might choose a recirc skimmer over a non-recirc skimmer.

Given the limitation of the size, I would be inclined to try decreasing flow rate for increased dwell time. Playing with the flow rate a bit is certainly worthy of experimentation for sure.

Plus...if you wanted to increase the chamber size, you can have my old G6 body if you like.

[golf nut]

Originally Posted by steveg

Hi there, so you are suggesting that the best way to operate a skimmer is to take water directly from the display tank and return it there instead of doing that from the sump?

I am suggesting that you have the sump turnover rate at the correct volume to get maximum results from the skimmer, typically this will be a lot less than the previously suggested 10x rate.

[sphelps]

Originally Posted by Mr OM

I am suggesting that you have the sump turnover rate at the correct volume to get maximum results from the skimmer, typically this will be a lot less than the previously suggested 10x rate.

But you can't explain why? Just cause, right?

[Canadian]

This is somewhat dependent on your sump layout but think of this analogy:

If I drop a small piece of sinking pellet food down my overflow and I have one of two options:

a) High flow rate through my sump
b) Low flow rate through my sump

Which one do you think is most likely to allow the intake/suction of the skimmer intake to pull in the piece of food? The one ripping the current past the skimmer or the one slowly plodding along?

I'd certainly rather pull mechanical chunks of organic waste out of my tank before they have a chance to break down and then become part of the chemical soup in the water.

[sphelps]

Originally Posted by Canadian

This is somewhat dependent on your sump layout but think of this analogy:

If I drop a small piece of sinking pellet food down my overflow and I have one of two options:

a) High flow rate through my sump
b) Low flow rate through my sump

Which one do you think is most likely to allow the intake/suction of the skimmer intake to pull in the piece of food? The one ripping the current past the skimmer or the one slowly plodding along?

I'd certainly rather pull mechanical chunks of organic waste out of my tank before they have a chance to break down and then become part of the chemical soup in the water.

While I see your view and get what you're trying to say two problems exist with your example. First a skimmer removes dissolved organics which I guess can be compared with food but we don't place organics/food in our overflow but rather rely on flow to get them there. So in real life that piece of food will get to the overflow faster if flow is higher, resulting in going to the sump sooner. Dissolved organics should be looked at differently than a food pellet, its concentration is distributed throughout the tank not in one particular location.

The second problem is the assumption less flow through the sump results in more water being filtered though the skimmer before going back to the display. First these are independent, the skimmer outputs the same as it takes in. So exactly how could one possibly determine how much overflow water is actually going in the skimmer and not simply bypassing it completely? With a lower turnover the amount of water being constantly recycled through the skimmer could actually be higher meaning less overflow water is going in compared to high turnover.

Regardless the point I'm making is that the two are completely independent. Dissolved organics are dissolved meaning the concentration throughout the tank will be virtually constant. The amount of organics taken in by a skimmer is essentially constant and independent from the water flow moving past it. High or low turnover (in limits), a standard in sump skimmer will work the same.

Lower sump flow rates are related to lower noise and less air bubbles but not skimmer performance. The only reading I've seen relating these two suggest higher flow rates as it will "keep solids in suspension, which increases feeding opportunities by fishes and invertebrates, and improves filter/skimmer opportunities to export such matter in a well-designed system"

[Canadian]

A good skimmer removes both DOC and solid particulate. For instance I've had shrimp molts end up in my skimmer cup. I want my skimmer to remove as much solid particulate as possible before it becomes DOC - hence the reason for not having a filter sock that requires constant changing.

[mr.wilson]

I agree with the idea that skimmers should be rated by bioload, but manufacturers are saddled with magic numbers that everyone in the hobby can understand. A better way to do it would be to measure water quality and compare it to a second sample taken 6 or 12 hours later. This would give you an index of decline and allow you to access how much equipment you need to keep it in check. Unfortunately that lowest common denominator is system volume not load. Some heavily stocked tanks are well balanced and subsequently put less demand on a protein skimmer. Other methods of nutrient export, chemical filtration and mechanical filtration also take the burden off of the protein skimmer. Protein skimming is limited to the removal of 80% of the available proteins and only 25% of the available TOC. For a proper evaluation of the abilities and limitations of protein skimming look here. http://www.advancedaquarist.com/2009/1/aafeature2

Protein skimmer design isn’t rocket science, but the only scientific formulas we have in determining size, contact time and bubble size are those offered by real life rocket scientist P.R. Escobal. His formulas have not been disputed to date and are summed up well in the following link http://www.hawkfish.org/snailman/skimmer101.htm

It is widely accepted that a two minute dwell/contact time is ideal for separating the maximum number of proteins and TOC (total organic carbon including both dissolved and particulate forms). This doesn't preclude the use of a protein skimmer that fits under your roof. In the case of a 400 gallon tank with a 1.33x flow through the protein skimmer, and a two minute dwell time, the contact chamber of the device needs to be 18 gallons. It sounds big, but so is a 400 gallon display tank, and you only need that size for optimum performance.

In addition to the comparatively low throughput rates recommended by Escobal (1.33 x per hour), protein skimmer manufacturers typically recommend 250-500 GPH throughput for larger units according to system volume and respective protein skimmer size. These specs typically equal 2 or 3 x the volume of the tank per hour and are chosen by practical trials rather than mathematical formulas. So why do some people disregard the recommendations of manufacturers and the formulas of rocket scientists in order to follow the 10x the volume of the tank guestimation of some kid working in an aquarium store?

The root of the 10x rule of thumb goes back to the days when we didn’t use closed loop pumps and we relied on a one pump system to keep detritus suspended (for feeding corals and collection in mechanical filters), to provide adequate gas exchange, and to deliver unprocessed water to filtration devices. There is no reason why we can’t pre-filter the water by collecting a thinner amount right at the surface air/water interface. This thin film is rich in surface-active agents (surfactants) that migrate to the air/water interface through the same process carried out in the protein skimmer. The practice of turning over large quantities of surface water draws a thicker intake from the display tank, thus diluting the hydrophobic (repelled by water) proteins we are trying to pre-filter.

The ideal system would collect a thin film of surfactants from the display tank and deliver it directly to the protein skimmer sitting in a sump (for safety/spillage reasons), after which it would be directed to the sump where the water can be further processed by a refugium, UV sterilizer, mechanical and chemical filtration methods, all of which requiring a similar slow throughput. The idea is to process all of the water thoroughly and only once before returning it to the display tank.

If your skimmer design doesn’t allow for a gravity feed, then the sump should be divided into two sections. One section holds the protein skimmer and the new unprocessed influent water, and the other holds water that has been processed by the protein skimmer reday fro further filtration and return to the display tank via a pump with the same output as the skimmer pump (less head loss). The water entering the first compartment by gravity or siphon from the display tank at the rate of “X”, can be pumped through the protein skimmer at the rate of “X” by a small feed pump. The processed water would exit the skimmer and enter the second compartment to assure it can only be filtered again after entering the display tank or in the case of the protein skimmer pump being greater than “X”. If the protein skimmer pump is less than “X” some water will bypass the protein skimmer, but the water will still only get processed once before returning to the display tank. The flow rate through the sump is directly related to the flow rate through the protein skimmer if you have an efficient first in first out (FIFO) plumbing system for your skimmer.

Refugiums, chemical reactors and UV units require the same type of flow volume so they can all be plumbed inline. In order to get a 99.9% kill ratio with a UV sterilizer, you can run no more than 4.16 gallons per hour per watt through it. In other words, a typical 30 watt UV unit should be fed no more than 125 GPH throughput, or the kill ratio will diminish accordingly. If you look at typical display tank and protein skimmer sizes you will find that the turnover ratios are about the same. Once again, P.R. Escobal’s formulas are considered to be the gold standard when sizing and establishing throughput for UV sterilizers. His UV formulas are summarized nicely here. http://www.aquariumadvice.com/articl...ers/Page1.html

The reason why you need to make sure your protein skimmer isn’t oversized is that you will have premature bubble popping which releases the bound proteins. As the bubble rises through the contact chamber it bombards the water passing in the opposing direction (down). The smaller the bubble, the more stable it is and the more likely it is to make it to the reaction chamber in the neck. Bubble stability increases as the bubbles bind hydrophobic proteins to form a skin. An oversized protein skimmer will cause premature bubble popping due to the lack of bubble stability. Proteins are both hydrophobic and hydrophilic (attracted to water) as they are polarized at each end. If the contact chamber is too large, the bound proteins will migrate back into the water.

Protein skimmers are primarily designed as chemical filtration, not mechanical. If you want to keep detritus, or a sinking food pellet suspended, it is the duty of a closed loop system, not the throughput. A throughput ratio of 10x will certainly not easily achieve this goal anyway.

The other benefits of following the scientific formulas and directly feeding protein skimmers is quieter overflows, no micro-bubbles and salt creep caused by oversized drains that lead to a sump compartment (ater goes directly to the skimmer where bubbles are welcome), less heat and noise from return pumps, better pod production in refugiums, a higher kill ratio for UV sterilizers, and better mechanical and chemical (longer dwell time) and mechanical (less bypass and breakdown) filtration.

The biggest problem in this hobby is the lack of effort hobbyists make to fine tune their existing equipment. Keep the glass on your lighting system clean, and spend less time "upgrading" bulbs. Use a smaller return pump and filter your water more thoroughly with fewer drain problems and better surface skimming. Plumb your skimmer right into your drain and get away from a "water mover" system that offers inefficient filtration.

[sphelps]

Originally Posted by Canadian

A good skimmer removes both DOC and solid particulate. For instance I've had shrimp molts end up in my skimmer cup. I want my skimmer to remove as much solid particulate as possible before it becomes DOC - hence the reason for not having a filter sock that requires constant changing.

While this might happen from time to time I assure you protein skimmers work on a molecular level and are not effective at filtering out particles greater than a fraction of a millimeter. The fact that it collected such items is more of a coincidence than a function. It will also only filter particles that float or are basically neutrally buoyant. This will also likely cause more maintenance requirements to keep your skimmer clean and working efficiently. Skimmers will work better for longer with a mechanical pre-filter. Quite simply you're just justifying an omission.

[sphelps]

Mr. Wilson, I'm slightly confused by your post and was hoping you could clarify.
First, only external/recirculating skimmers have an adjustable turn over rate and none are traditionally gravity fed, unless by gravity fed you simply mean with a pump because no skimmer should be run off gravity (such as straight from overflow) as it will never produce constant flow and cause the skimmer level to be either too high or too low. Also building a separate skimmer chamber which requires a pump to feed water out at the same rate of the skimmer is a new one for me, I have never seen this. The 10X turn over recommendation is based on tank/sump flow and not skimmer flow, I have never heard of someone running 10X tank turnover through a skimmer before. Today's skimmers are not co-current, air stone powered tall structures. They mostly use a single pump and do not offer flow control. Lastly sumps should be designed to handle the tanks/owners requirement for flow, this is fairly simple and eliminates things like mechanical filtration bypass and would provide adequate contact time for carbon.

[lastlight]

Mr Wilson that was awesome. Thx for taking the time to share that.