So I wanted to write an article around some of the more common topics and questions that come up about skimmers. Once again, a disclaimer: There are many people in this hobby that are much smarter than me, have much more experience, and have seen all the fads come and go. I am a sucker for gear, and I have read and talked to some of them. I am not trying to put myself in the same league as them, I am just trying to share some of the things I’ve learned along the way. For those new to the hobby, or those that need a refresher, here is an article by one of “those guys” to bring everyone up to speed as to what “skimming” is. No need to rewrite what Randy Homes-Farley wrote long before I got to this hobby. What is Skimming? by Randy Holmes-Farley - Reefkeeping.com Now that we are up to speed on the air/water interfacial area ;D, let’s talk about the machines that make them. Skimmer Types There are many ways to make a bubble machine. Any way to inject air in water will do. Any way we can chop it up will be better. There are still plenty of “old school” skimmers being used… venturi skimmers and downdraft skimmers, probably still some air stones out there bubbling. Here is a quick Wiki link to the various designs if you are interested. (wiki link Protein skimmer - Wikipedia, the free encyclopedia) For this article I want to focus on needle wheel skimmers. I feel safe saying they are the predominate skimmer being used these days. Before I go on though, we need to discuss the various ways to introduce air today. • Venturi: A venture is a principle that says if you increase velocity of a fluid with a nozzle, you can create a low pressure area. Blowing air across a straw and drawing up Coke into the straw is the easiest example I can think of. Older Venturi skimmers would pump water across some sort of convergence, and draw air in and the air and water mixture would then go to the skimmer. Today, we still use venturis, but we put them on the inlet side of the pump. • Spray injection. (AquaC): Most folks that have ever washed a car knows that if you make a nozzle, (thumb over a hose) and spray it into a bucket of water, you make bubbles. That is basically spray injection. AquaC uses a patented spray nozzle to shoot water into a body of water and produce bubbles. You need a strong pump to make it work, the stronger the better. • Beckett Skimmers: A Beckett valve is a venturi type valve that has 4 ports that draw air. They were first used in the waste water field. Most notable uses are by Precision Marine and MRC. Even DIY’ers can make a Beckett skimmer. Again, Beckett skimmers need strong pumps to operate them efficiently. Water is pumped into the valve where a low pressure area draws air in through the multiple ports. Differences between types Becketts and Spray injection requires a lot of pump. The air draw and bubble quality are actually very good. They tend to need more adjusting. You can change water level and you can adjust air draw. With bigger pumps, you use more power and add more heat. Venturi skimmers could draw plenty of air. What has changed today is the needle wheel impeller or pin wheel impeller. By placing the venturi on the inlet side of the pump, we can use a pin wheel impeller to shred the air water mixture further. Since the pump is now moving an air water mixture, power use is dramatically lowered. So the dominance of needle wheel skimmers isn’t because they can make better bubbles, it is because they can do the same job with much less power use and heat added. They are also much simpler and do not require air adjustments. Plenty of folks modify their impellers for even greater performance. (mesh mods) Skimmer construction. Skimmers are not some plastic tube that someone slaps a pump on and it makes bubbles. Body size, neck size, neck length, how much air and water the pump moves all needs to be balanced. If these variables are not well balanced, you will have a poor performing skimmer. • Reaction chamber: The air water mixture enters the body from the pump. This is where the DOCs and air water interface mix to collect the organics. Proper size ensures enough contact time for attraction. • Transition area: This is where the body diameter is reduced to meet the neck diameter. You want a smooth step less transition in order to not break the bubbles that have been collecting DOCs. A nice gradual decrease or smooth radiused transition are best. • Neck: once the organics are attached to the bubble, they need to be collected. As the bubbles rise, they are moved up by the air flow in the neck. Excess water drains off the foam and it is then collected. • Collection cup: Once the foam is collected, it needs to be removed for disposal. Not much to a cup, the bigger the better. Just about all skimmers these days have a deflector to point the foam down into the cup. Air holes in the lid allow all the air that was used to escape. Latest improvements The drive in skimmer design recently is to reduce turbulence. In the past, it was thought that you want as much turbulence as possible. This was to increase contact time in the reaction chamber so that the DOCs could be stripped from the water. However, if you have a bubble that is already saturated, and it crashes into another bubble and is destroyed, then you have ruined what you were trying to obtain. It is thought today that the mixing by the pump, and the injection into the skimmer produces contact time. By reducing the turbulence in the reaction chamber, you allow the bubbles to become saturated and transport those DOCs up to the neck. Maintaining a smooth step less transition helps the delivery. • Bubble plates: When the air/water mixture is injected by the pump into the body, it is usually at a 90 degree angle. Bubble plates are used to redirect that flow upward and to reduce turbulence inside the skimmer body. Not all bubble plates are equal. Hole size, plate thickness, and number of holes all play a part in the plates effectiveness at doing it’s job. Just some perforated piece of plastic slapped on top of a pump is not good enough. Just about all quality skimmers these days have this feature. • Cones: Cones skimmers are the latest greatest. Cones are not a fundamental leap in technology, only a refinement of an existing design. The cone is used to reduce turbulence further. The gradual taper is very good at maintaining the bubbles as they rise in the chamber. The transition is very gradual and the movement into the neck keeps the foam head very stable. All things equal, a cone will perform better, but a well balanced cylinder will easily do better than a crappy cone design. Production costs While a reef tank can be quite an expensive hobby, it does not need to be. However, quality costs money. There are quality skimmer designs at every price point. The more expensive you go, the better the materials are, the more features you get, and the ease of use is better. Nothing illustrates this more than the Rolls Royce of skimmers, Bubble King. Lots of machined PVC, lots of thick cell cast acrylic. The balance and design are top notch, and the Red Dragon pump is arguably the best pump on the market. Absolutely beautiful. Darn thing is worthy of a museum. However, they are quite expensive. And like all things luxury, the laws of diminishing returns applies. Bubble Kings perform very well, but they do not perform twice or triple as others that cost half or a third. Cone skimmers deserve a mention. Most complaints aired about cones is that they are too expensive. You may be surprised to hear that a cone body actually cost less to produce than a cylinder body. So then why the higher price? The fact of the matter is that the cone skimmers introduced to date have been quality skimmers with top notch construction. Premium skimmers offered by premium manufacturers. ATB, Warner Marine, Vertex Alpha to name a few. Plenty of other companies are now joining the ranks of cone producers. Most cones are the top of a manufacturer’s line. SWC, Octopus, and Bubble Magnus to name a few offer very good performing designs at a very affordable price. Pumps Now that we have talked about the body and production costs, it is time to move to the heart of the skimmer, the pump. The pump is the most important part of the skimmer. Personally, I would choose one skimmer over another on pump alone. You want one that has low power consumption, low noise, high reliability, and is cheap. All those other things do not come with cheap. There are no real skimmer pump manufacturers per se. Pump makers modify their water pump motor blocks for use with needle wheel impellers. Let’s talk about some of the various pumps used. Ehiem: Some Ehiem pumps have been fitted with needle wheels impellers. Ehiem has a very nice reputation for a quality pump. But most companies have either not used them, or stopped using them. Price may be one reason. I’m not entirely sure what some of their numbers are. I know ATB used to use them on their Small skimmers, (now 840) but have since moved to Sicce pumps. Laguna: Laguna makes pond pumps and is owned by Hagen. These are very nice pumps with nice electronics. Companies that use their motor blocks are ATB’s AirStar, Bubble King’s Red Dragon, and SWC’s Askoll. They are very nice pumps, proven, quiet and powerful. These pumps are modified with custom impellers, custom volutes and venturis. Air draw is 80-100 scfh with the most common 1500 motor block. (Bubble King makes bigger Red Dragon pumps using bigger motor blocks) These pumps can easily handle 200-350 gallon tanks. Prices range from $250 for Askolls, all the way up to $450 for Red Dragons. Sicce: (pronounced See-chay) Sicce is an Italian company that produces pond pumps. The most common skimmer pump is the PSK-2500. There are a ton of them out there. They are reliable, quiet, and very efficient. Relatively inexpensive, they can be bought retail replacement for around $120. Makers using them are plenty: Warner Marine, Octopus, SWC, ATB, to name a few. They can generally do anywhere between 700 lph- 1100 lph The big deal with Sicce pumps: So the pump is a water pump. As a water pump, the dynamics of the impeller and water make the impeller start in the right direction. With AC power and magnetic pumps, they can start in either direction. The stock Sicce water pump volute is directional. Meaning it is made to move water in the right direction with the least resistance. See the difference between the top and bottom of the outlet in this pic? The problem is, with a needle wheel impeller, the dynamics change, and the impeller can start backwards. No big deal, but with the air/water moving backwards, the volute causes drag, and the performance suffers about 20%. Not the end of the world, but it is an issue. ATB Mini AirStars, and Tunze Hydrofoamers have custom volutes that are non-directional. So it does not matter what direction the impeller moves, the performance is the same. SWC, Octopus, Warner Marine, ect. use stock volutes. Personally, I don’t find it to be a big deal. If it starts backwards, I can tell just by the sound, or where the bubble level goes to. However, there are some that flat out refuse to use a Sicce for that very reason. You will have to figure out how much it matters to you. EDIT: Sicce put out a new pump that puts out the same numbers as the PSK-2500 but does not have any start up issues. It's done with microprocessors not just a non directional volute. So it starts right all the time. It's a 600 or 800 model number. So look for that on new skimmers that run Sicce pumps and you will be good to go. Tunze Hyrofoamer: The Hydrofoamer is actually a Sicce motor block. Tunze then goes on to make a different impeller with stronger magnets and makes different volutes for it. Different enough to call them a different pump. Nice pumps. Cost a bit more at $190. Air draw is from 800 – 1300 lph. Although, I have not verified that in the real world. With the modified volute, there are no directional start issues. Hydrofoamers can be bought individually or as an option on I-Tech skimmers. Chinese pumps Bubble Blaster: This pump is put out by Octopus which is owned by Coralvue. The pump is a purpose built needle wheel pump made in China. The pumps hit the market at the end of 2009. So far (6 months) they have been warmly received. They have all different sizes from HY 2000 for 90g up to HY 5000s for 300g tanks. I think they have bigger too, 6000s and 8000s. The BB 3000 is directly comparable to a Sicce 2500. The BB 3000 will do slightly more than the best Sicce. The BB 5000 is directly comparable to a Laguna 1500 based pump. Askoll, Air Star…. The numbers are comparable for power draw, and performance. The pump has some nice features like special anti-lime coatings on the shaft and powerful magnets. Most folks have been quite happy with their performance. However, while they can be compared to Sicce and Lagunas, they seem to be more noisy. Most folks that have a lot of experience with all the pumps say they are not the most quiet. Also, reliability is still a big unknown. They come with a 3 year warrantee, but how else are you going to get people to buy a new product if you do not cover them well? Size wise they are very big compared to other pumps. And these are not cheap. Only slightly less than a Askoll, and more than a Sicce. However…. Having said all that, these pumps seem to be a HUGE hit for Super Reef Octopus. I applauded any company for producing purpose built skimmer pumps in a variety of sizes. These are not cheap Chinese pumps, they are well built Chinese pumps. As long as the reliability is there, these pumps will be great. I only hope they force other companies to compete with the same. We will all win. Atman: ….honestly, this is a cheap pump. However, cheap does not have to mean poor performance. Manufacturers are simply giving what the public want….low cost. Atmans have been used in Bubble Magus, and SWC skimmers. They actually have good performance, and they are reasonable quiet. As in “quiet”…not quiet for how cheap they are. They have been reliable too. So over all, these have been very good pumps to get cost down and still provide good performance. Resun: these are used by Vertex. They initially had some shaft problems, but that has been taken care of. They have good performance and have been very reliable since the initial problems have been solved. Pump Modifications. Needle Wheels: ATB made a Purple Pin Wheel for their Mini AirStar pump. The PPW will fit any Sicce pump, and does not require any different parts. The wheel is a bigger diameter than the stock wheel, and has had some start issue. Too big to turn. The solution is to blow in the air tube to help it get going. Actually, the problem is not that wide spread and there are a lot of these wheels out there and they are very popular. They offer better performance over stock wheels. Warner Marine introduced the Red Demon wheel not too long ago. It has a smaller diameter than the PPW, and longer pins. The performance is the same as the PPW, and it has not had any start issues. I run one on my Sicce and it offers a 20% increase in air draw over stock. You do not need any other parts, it is a direct replacement for any Sicce pump. Mesh Mods: OK…. I am not the guy to talk to about mesh mods. I personally have no desire to mesh mod anything, but this is how it works. You cut the pins off your needle wheel, and then attach some sort of mesh to the plate with fishing line of small zip ties. Mesh modding most definitely gives better performance over the best pin wheels. Sicce pumps with mesh mods have gotten 47 scfm. However, as the mesh breaks down, so does the performance. Mesh wheels need to be redone about every 6 months. Also, some folks do not do it right, and cause quite a few start up problems. In fact, Sicce had a bad reputation for startup problems. But it had nothing to do with the pump, it was all due to the modifications people were doing to them. There are plenty of tutorials out there how to mesh mod your pump. It is effective, and can be done right, I just personally don’t see the need for it. I do everything I can to minimize maintenance on my system. Reducers/Volutes: MSX and Warner Marine make their own reducers for Sicce pumps. To get the most out of the Red Demon wheel, you can use WM reducers. However, you might have to buy a new volute. ATB offers their volute separate for any Sicce pump. It is quite pricey for a piece of machined PVC at $150. But it does come with a PPW too. It solves the directional start issue. Pumps: Popular pump replacements are Askols and Bubble Blaster. Lots of folks are using these for better performance over dual Sicce skimmers. Bubble Blasters seem very easy to use as replacements for various skimmers. Heck, maybe I’ll even try one. OK, enough about pumps! They are important. The pumps get better as the prices go up, but honestly, there is no pump I would steer anyone away from. I mean I might recommend one over another, but there are no pumps in any reputable skimmers I would tell you to stay away from. So let’s move on to skimming. Skimmer Ratings So how do we size a skimmer to a system? Well first we get some chicken bones, then we get into a VooDoo trance. Throw the bones in some tea leave, and have someone read our palm. ;D OK, not really, but it seems to be quite confusing. There is absolutely no rule of thumb, or any type of rating that says this size skimmer with this much air will do this system. Part of the problem is that there is absolutely no standard in what a “bio-load” is. Every aspect of the skimmer is going to determine how well it will perform and what it can do. The body size for contact time, the air water ratio the pump does, the transition to the neck, the size and length of the neck all play a part. So how do you as the consumer figure out what size you need…. Well you don’t. You are basically at the mercy of the industry. However, it is not as bad as it seems. Most reputable companies and sellers are very knowledgeable these days, and they are very reasonable in ratings. In days gone past, crappy skimmers were guaranteed to handle a 1000 gal tank. Total nonsense. There are still some today that are quite over rated, but I don’t want to name names and hurt feelings. Most of the popular brands and popular vendors got that way by giving a solid product rated for what it does and sold by knowledgeable people that are good at matching equipment to systems. For needle wheel skimmers, about the only rule of thumb around is a 500-600 LPH per 100g of water. That is about as handy as watts per gallon, but it is all that is out there. And that isn’t absolute, any crappy skimmer with that number will still be crappy, and there are some outside of that number that are very well designed and still perform well. If you shoot for that number, and you are looking at well performing, tested, popular skimmers, you are in the ball park. Here is a thread I started on another board that I discussed ratings with some manufacturers. It is a good read. http://www.reef2reef.com/forums/lig...cussion/37593-skimmer-ratings-discussion.html Skimmer Sizing Let’s get this clear to start. What we are rating for is how much bio load the skimmer can handle. Yet there is no such standard for bio load. We can talk about stocking levels, but even that is pretty murky. A skimmer can handle a bigger tank if it has less fish in it. But let’s just be honest, who stocks a low stocking level? 90% of us end up with a heavy bio-load or stocking level for our tank size. So let’s just all get on the same page. When we are talking skimmer ratings and sizing, we are talking heavily stocked tank. Adjust accordingly if you do not like a lot of fish. So the thinking goes… if 500 lph of air per 100 gallons is good, then 1500 lph per 50g of water will be 6 times better!!! UHHH… NO! One of the most common questions is how big should I go? There is no good reason to get a skimmer rated for bigger than your system. Bigger skimmers do not pull out more organics. Let me say that again…..bigger skimmers do not pull out more organics. What a bigger skimmer does is give you more head room. So if you have a 100g and your skimmer can do 125g and you have a fish die and rotting in the rocks…. Your skimmer will have the extra capacity to handle that. Once the organic concentrations get so low, the foam head in the skimmer will collapse and you will no longer be removing organics. The easiest way to explain this is that if you have a100g system, with a 100g rated skimmer, your skimmer will be working 100% of the time. If you then put a skimmer on your system that is rated for a 200g tank, it would not do a better job, it would only have to work 50% of the time. Here is the real kicker…. Huge skimmers on tiny systems actually perform worse than a properly rated skimmer on that system will work. The neck on big skimmer is so large that you can’t maintain a proper foam head with so little organics to work with. So your system sits there unskimmed until enough organics build up that the large skimmer will puke a bit into the cup and shut down again. So then how Big??? Honestly, I want 125% of rated. Just for some head room. 150% bigger max on any regular system. Now a popular rule out there is to buy a skimmer twice the size of your tank. The most a skimmer can span is around twice the size. So you can run a skimmer rated on the low end of 100g and on the high end 200g. However, the only good reason to do this is IF you know you will be moving up to a bigger tank in the near future. And even then, the most a skimmer can span is twice the size. Any more than that, and the skimmer will perform terrible on the low end, or not do enough on the high end. If it is temporary, and you got a killer deal on a monster skimmer for your next tank, take the deal. Just know what you are doing. But if you just moved up to that big tank, and you will be there for years to come, get a skimmer rated for your tank. Can you over skim a tank??? Simply… NO, you can’t overskim tank. There are some that believe you can. When I have asked for explanations, I have received none. There are some corals that can thrive in high nutrient water. Low nutrient water may not be enough. That just means you needs to feed more. Skimmers do not remove 100% of dissolved organics, they only remove those DOCs that are water phobic (attracted to air). They also remove particulate matter just by getting caught up. One thing a good skimmer does for us is gives us the ability to feed more and still maintain low nutrients. To go even further, some resort to vodka dosing and other methods to go ULN (Ultra Low Nutrients), in SPS tanks and their systems do well. The trend has been for bigger better performing skimmers on demanding SPS tanks and the tanks have gotten better not worse. Finally to Operation. So you did tons of research, you asked a ton of questions, you got the skimmer you want, the pump you want, the size you want, you slapped down the plastic and the Brown Santa just left your drive way…… WAHOOOO!!! Now what? First, take a minute to admire the beauty of a new clean kick ass skimmer. Now lets get to covering it in poop. Some recommend a vinegar bath. Run the pump and skimmer in a bucket of vinegar for a while. I have never bothered, but it is a good idea. The new skimmer will have oils on it from manufacturing. This is part of the break in, but the vinegar bath will remove those and speed up the break in. The break in process: The skimmer needs to get slimed up like everything else in your system. It will develop a coating and the skimmer will perform better. Most skimmer will start producing skimmate within 24hrs, but break in continues for at least a week up to 2 weeks. During this time, the skimmer will perform better and better. If you didn’t do the vinegar bath, the oils will inhibit the foam head until they are broke down and removed. Initial Setup: Personally, I like to go right in the middle of manufacturers recommendations. I will usually error on the deeper side. I like wet skimate over dry. It’s best to shoot for the middle. Until the skimmer is broke in, there really is nothing you can do towards final setup. Skimmer Depth: The depth of water a needle wheel skimmer sits in has a huge impact on performance. It isn’t because of how much the skimmer is under water, it is because of how much of it is above water. The column of foam and water above the water level has a weight, and that weight puts back pressure on the pump. That backpressure decreases the air and water draw the pump can do. So the higher the water level in the sump, the less above water, the less backpressure, the more air and water the pump will do. Now that means that the bubbles will be higher in the neck, the skimmate will be wet, the skimmer will process a lot of water. However, not everyone likes wet. So to get it dryer, you put the skimmer on a stand and move it up. The more above water, the more backpressure the less air and water the pump will move. The lower the bubbles in the neck, the dryer the skimmate will be. What you want is a balance between how much the skimmer will process and how you like your skimmate. This is very important. Now we have said all that, there is no skimmer out there that performs well is an inconsistent water depth. You have to have a consistent water level to get consistent performance. Either set the level with a baffle, or set it with a ATO. Water outlet: Once you ball park the depth where you want it, you fine tune the level with the water adjustment. Wedge pipes work fine, gate valves are better. Ball valves are not very good for this application. Adjust the water level to “backup” or let out more water. This will raise/lower the water level which will raise/lower the bubble level and foam head. The bubbles should be breaking mid way up the neck. From there you can fine tune for what you want. Wet or Dry Skim: This is a very popular subject. There is quite the following that believes the darker the skimmate, the better the performance. Judging skimmer performance by skimmate color is like saying a Honda Civic will beat a Porche GT3 because the Civic is red and Porche is blue. In the article I linked to earlier about skimmers by Randy Holmes-Farley, he made the argument that wetter skimmate removes more organics. That less drain away like with dry skimmate. Yet to me, that does not mean they are not still removed later. When I recently asked him for clarification on the subject, he said he never meant it to mean that is what happens or that he has data to prove it. It is just that his thinking is wetter “should” remove more organics. The argument remains that darker means better performance. No, darker just means more concentrated, not more quantity. The truth is, wet and dry may very well remove the same. That once the organic is bound up in the skimmer, it is effectively removed from the system regardless of if it is in the cup or not. And that the amount of water drained from the foam does not make a difference on total organics removed. However, those that argue that the blackest most concentrated skimmate is the sign of peak skimmer performance have absolutely no argument to back it up, or evidence to settle the issue. The fact is, wetter skimmate simply has more water in it, and you will have to empty the cup more. It will also keep the neck cleaner. Dryer skimmate will be more concentrated and require less dumping. Yet with the bubble level lower creating dryer foam, more waste will accumulate in the neck and require more cleaning. Feel free to produce whatever foam tickles your fancy. I have always stuck to the wetter side. One note of importance…. The more air skimmers move these days, the more water is evaporated. My skimmate in the cup is always tea colored, yet I can look at the foam and tell it’s dry. One important thing to remember is that there is a lot of moisture that will condense on the cup. It runs down as fresh water and dilutes the color of the skimmate in the cup. Don’t get so hung up on skimmate color. Just look at your foam and make it as wet or dry as you want. Also, I have had white and black skimmers. On my same system, skimmate looks like tea in a white cup, and it looks like coffee in a black one. Don’t let the cup color fool you. WHEW!!! That is about all I can think of for now. I hope this has answered some questions, or better yet, gave you some new ones. I will try to add to this when I have any new info. This is not my thread, it is 3Reefs. I would love any additional advice or experience you may have on the subject. Perhaps those with Becketts, or spray injectors can add their two cents on what they like. Happy Skimming!