To skim or not to skim that is the question. I have head many conflicting reports on the use of skimmers while employing an ATS. I know the so called con's but think they may be over exaggerating the amount of "good stuff" they remove from the water. I have yet to read/see any scientific to back up the claim not to run a skimmer only some people who don't run skimmers with an ATS but many still do so. I turned my skimmer off for 2 weeks and apart from some red cyno appearing on my sand I noticed nothing else either good or bad. However when I turned my skimmer back on it pulled out a good about of foul smelling gunk. If anybody knows of any REAL scientific studies that have been published on ATS along with skimmers I would like to read them.
Hi atoll, hope the following info helps; keep in mind that TOC is Total Organic Carbon, which is Particulate Organic Carbon plus Disolved Organic Carbon (DOC). DOC is what skimmers are supposed to remove. The last paper below sums up nicely what skimmers DO remove. Feature Article: The Development of a Method for the Quantitative Evaluation of Protein Skimmer Performance By Ken S. Feldman, Kelly M. Maers, Lauren F. Vernese, Elizabeth A. Huber, Matthew R. Test Department of Chemistry, The Pennsylvania State University Feature Article: The Development of a Method for the Quantitative Evaluation of Protein Skimmer Performance Extract from Conclusions Quote - All four skimmers were quite similar in the second performance figure-of-merit, the total amount of organics removed. The skimmers typically removed greater than 80% of the BSA. In contrast, perhaps one of the more interesting observations to emerge from these studies is the fact that all four skimmers tested removed only 20 - 30% of the total organics present in authentic reef tank water. Feature Article: Further Studies on Protein Skimmer Performance By Ken S. Feldman, Kelly M. Maers Department of Chemistry, The Pennsylvania State University, Feature Article: Further Studies on Protein Skimmer Performance Extract from the Conclusions Quote - A perhaps more interesting observation to emerge from these skimmer studies involves not the rate of TOC removal, but rather the amount of TOC removed. None of the skimmers tested removed more than 35% of the extant TOC, leading to the conclusion that bubbles are really not a very effective medium for organic nutrient removal. Feature Article: Bacterial Counts in Reef Aquarium Water: Baseline Values and Modulation by Carbon Dosing, Protein Skimming, and Granular Activated Carbon Filtration By Ken S. Feldman, Allison A. Place, Sanjay Joshi, Gary White Feature Article: Bacterial Counts in Reef Aquarium Water: Baseline Values and Modulation by Carbon Dosing, Protein Skimming, and Granular Activated Carbon Filtration Our earlier research on the topic of carbon nutrient levels in marine aquaria (Feldman, 2008; Feldman, 2009; Feldman, 2010) has provided experimental documentation for four conclusions that impact on TOC management in our reef tanks: 2. Protein skimming (i.e., bubbles) is not very effective at removing TOC from aquarium water, depleting typical reef tank water of only ~ 20 - 35% of the post-feeding TOC present. 3. Granulated Activated Ccarbon filtration is quite effective at stripping reef tank water of its TOC load, removing 60 - 85% of the TOC present. 4. And, quite intriguingly, the natural biological filtration, which starts with bacteria and other microbes, is remarkable in its capacity to remediate reef tank water of TOC, easily removing 50% or more of the post-feeding TOC increase in tank water. Further - Overall, the major conclusions from these carbon dosing experiments are - Addition of a carbon source to an active reef tank via a recommended schedule does not lead to any measurable increase in water column bacteria load. Interestingly, even though the bacteria population starting points in the KSF tank water skimming experiments (Figs. 19, 20, and 21) and the SJ 55 skimming experiment were very different, in all cases, only about 28-39% of the original bacteria were removed before the data "flatlined". It is likely a significant observation that there is a floor in aquarium water bacteria populations that skimming will not breach. Further – there appears to be two functionally distinct populations of bacteria; one that is susceptible to bubble-based removal, and one that is not. What is this functional difference, as far as the skimmer is concerned? An earlier publication describes the limitations of bubble-based mechanisms in scrubbing TOC from aquarium water (Feldman, 2009). The argument forwarded in that case may very well apply here as well, Fig. 23. It is plausible that the requirement for hydrophobic patches on particles (i.e., bacteria, TOC molecules or clusters; refer to Bacterial Surface Charge and Protein Skimming, Section 1.2 above) that must be met for successful bubble-based extraction may only apply to some but not all of the aquarium water column bacteria (approximately 28-39%, by our studies). Thus, there may be some discrimination by the skimmer based upon bacteria surface properties. In addition, some but not all bacteria form multicellular clumps (flocs) that may be susceptible to foam-based extraction based upon simple buoyancy and not bubble-surface chemistry; once again, this physical process constitutes a basis for selecting between different bacteria types. So, the bottom line appears to be that some but not all bacteria can be removed by protein skimming. Further – Is "old tank syndrome" related to possible nutritional deficiencies stemming from this bacteria "gap"? Alternatively, could "old tank syndrome" be symptomatic of a gradual decrease of bacterial diversity as a consequence of selective skimmer-based removal of only bubble-susceptible bacteria? Feature Article: Elemental Analysis of Skimmate: What Does a Protein Skimmer Actually Remove from Aquarium Water? Feature Article: Elemental Analysis of Skimmate: What Does a Protein Skimmer Actually Remove from Aquarium Water? By Ken S. Feldman Feature Article: Elemental Analysis of Skimmate: What Does a Protein Skimmer Actually Remove from Aquarium Water? Conclusions The chemical/elemental composition of skimmate generated by an H&S 200-1260 skimmer on a 175-gallon reef tank over the course of several days or a week had some surprises. Only a minor amount of the skimmate (solid + liquid) could be attributed to organic carbon (TOC); about 29%, and most of that material was not water soluble, i.e., was not dissolved organic carbon. The majority of the recovered skimmate solid, apart from the commons ions of seawater, was CaCO3, MgCO3, and SiO2 - inorganic compounds! The origin of these species is not known with certainity, but a good case can be made that the SiO2 stems from the shells of diatoms. The CaCO3 might be derived from other planktonic microbes bearing calcium carbonate shells, or might come from calcium reactor effluent. To the extent that the solid skimmate consists of microflora, then some proportion of the insoluble organic material removed by skimming would then simply be the organic components (the "guts") of these microflora. These microflora do concentrate P, N, and C nutrients from the water column, and so their removal via skimming does constitute a means of nutrient export.
Thank you, all very interesting. I read something a few years back (not sure where) where an analysis of skimmate revealed a high concentrate of alga and diatoms. IMO even 30% removal of organic matter is a significant amount. However as not ever tank nor system is the same then different tank setups may remove more of one thing than that of another tank. What my question is however is a simple one. What effect good or bad do skimmers have on the performance of an ATS when used together and how significant running an ATS with a skimmer be? Like I posted above, I stopped running my skimmer for 2 weeks but noticed little effect on my tank. Not sure how old the following is. Skimming Basics 101: Understanding Your Skimmer by Frank Marini, Ph.D. - Reefkeeping.com
That's a good summary @TbyZ, thanks for putting that together Most of the current information about algae scrubbers is rather anecdotal, to my knowledge. There hasn't been much intense study done since the 1980s really, at least not of any scientific bearing. I think this will likely change in the near future as some of the players in the skimmer research you referenced are now looking at and toying with algae scrubbers - at least one of them was at some point recently. The AA article is always a good one because it revealed (not sure if it was the first time) that there are likely skimmable and non-skimmable bacteria, and due to this, relying on only skimming could actually cause secondary issues over the long term (i.e. the effects of removal of one primarily only class/type of bacteria). I think it's probably too early to draw any conclusions but it certainly does raise some interesting questions. From what I've seen, some of the better overall systems rely on a diversity of filtration systems. This seems to be more prevalent in larger tanks where the owner buys into the mindset that having more than one system makes sense, as they provide multiple layers of protection for the investment. When it comes to smaller systems, like <150-200g, that's when it seems that people tend to choose one type of filtration as "primary" and then anything else is just secondary to that main method, if there is anything else. That is mainly due to industry influences about what you should use, as well as limitations of space. If there was a way to rate every piece of equipment or media based on a more real-world factor instead of just tank volume, it would be much easier to develop a custom setup that allows for diversity without taking up a ton of space. I'm referring of course to the feeding guideline...feeding is by far the primary input of nutrients into a closed system. Supplementation of chemicals to account for growth is really not a factor, and aside from those 2 things, you're really left with top-off for evap, and whatever is in your salt mix for water changes (which is a combination of top-off and supplementation, in a way)
You confirm much of what I suspect regarding real dependable information and much is simply anecdotal with little or no real scientific back up. Maybe somebody like Danna Riddle to investigate deeper into. BTW do you run your just ATS's on your own tanks without skimmers?
On my personal tank, 120g, scrubber only (L2). I have overstocked it and I overfeed however and need to either get rid of some fish and cut back on feeding, or put a bigger scrubber on it. It's a bit of a tester setup, basically seeing what happens when I try to push things as far as I can, or be as lazy as possible when it comes to maintenance! On one other tank I help maintain, 144 custom, also scrubber only (L2), but they feed a bit less and have a few fewer fish, and that water is in great shape One other tank that did have an L4 on it until the pump died for the 2nd time and cooked the screen, is a 200g with a moderate to heavy load, moderately to sparingly fed (considering the size of the king of the tank, which is a 10" Vlamingi Tang), and a filter sock, NWB-150 skimmer, and some carbon (which is not frequently changed) and bi-weekly to monthly 20% PWCs and that tank water is in excellent condition. The scrubber actually was getting less growth than either of the L2s, in fact it rarely had "stellar" growth cycles, it was always kind of gooey mixed in with a GHA base. My take on that was the scrubber was somewhat starved and oversized, so after that pump died (during an extremely busy time period) I decided to remove it and put an L2 in it's place and teach the owner how to maintain it (the space made maintenance kind of a pain for a Rev 3 L4)
The theorectial fundamental purpose of a protein skimmer is to remove Disolved Organic Compounds (DOC) before they are mineralised into ammonia. This is meant to take the load off the biological filtration - less ammonia = less nitrate. Mechanical filtration takes care of any significant particulate organic matter. But as the links I posted above show, skimmers remove only about 30% of Total Organic compounds, & that is almost totally Particulate Organic matter, ie, food, not Disolved organics. So a skimmer is not technically functioning as theorectically proposed. Not to worry, because an algae scrubber uses ammonia, ammonium, nitrate & nitrite as a source of nitrogen (as well as phosphate). So, whatever unvalidated & mysterious claims are made for using a skimmer, nutrient control, certainly as far as nitrate is concerned, and in my case, definately not PO4 either, is not valid. Thinking about DOCs, a certain content is necessary as they are food for bacteria & corals. Although you don't want levels that are too high, having levels that are too low, if possible in a normally functioning aquarium, would be worse. Controlling them is easy enough; - water changes AND especially activated carbon, is all you need. I run a scrubber, activated carbon & use a filter sponge 50% of the time. I haven't used a skimmer for quite some time, and there was no negative effects when I stopped using a skimmer.
Whenever I recommend using a skimmer, I suggest 2 things: considering sizing it per feeding, and skim really dry. This is of course really tricky and there is no study behind how to size a skimmer for feeding. Everyone sizes them per tank volume, which really does not make much sense but it's really easy to convince someone of what size they need based on a simple number they have without thinking about it, vs having to examine the input to the system. The starting point for me anyways is a skimmer that is "rated" at 1/2 of the size of your system. That paired with a scrubber rated for what you feed and your skimmer is likely already oversized but at least it's not yuuugely oversized. Then, skimming dry allows you to get the benefit of aeration (which there is a rather important benefit here that is often overlooked) without ripping all the food particles out (most will recirculate) and making sure you shut off for an hour after feeding. If you decide to remove the skimmer, I recommend doing so in stages by reducing hours one or two times per week over a period of months. If your skimmer doesn't flip out when you re-start it, this works pretty well. I don't know of anyone directly that has made a device that essentially just aerates the water just like a skimmer but doesn't perform the skimming function, unless you start looking into the nano bubble concept (which has less to do with aeration)
'aeration' is apparently the theory Randy Holmes Farley came up with to justify using a skimmer after proper studies showed how poorly skimmers really performed. Doesn't an algae scrubber aerate the water to a much greater extent, through photosynthesis. And also through the exchange of gases via the air - water interface, created by the thin wall of water flowing down the screen. A third mechanism would be the water falling from the screen, splashing into the sump water. No doubt a skimmer aerates the water, but I believe a scrubber does a more througher job.
Interesting thread and thanks to TbyZ for the links (just finished reading all of those articles, phew). Perhaps Skimless setups can introduce an air pump that is run for only short periods (1-2 minutes), on a periodic basis (every 60 to 90 mins) to provide aeration. (I think there is a guy on reefcentral who does this and claims it is beneficial to he's setup) One could even go one better and have an airline tube inserted into the in-let of the pump feeding the ATS to benefit to periodic aeration. Would this last point have any benefits to the growth of the GHA in the ATS?
I guess I'm of the opinion that while a scrubber can definitely infuse air into the water due to the nature of the beast, how much is infused depends on exposure as well. An open-air screen would have more exposure to air than a closed unit, but a closed unit has a bit of a growth advantage (3D effect). I've had a few people replace the lid with one that incorporates a fan, but not enough people trying that to make a definitive conclusion of any kind Then @Garf did his infamous experiment where he bubbled CO2 directly into the intake of the scrubber. I'd have to dig up the thread where he did that...
It is interesting to consider that the aeration from a skimmer is meant to expell excess CO2. But there would never be excess CO2 in a tank with a properly functioning scrubber. Quite the opposite. So I expect, in that case, any aeration would increase CO2 because the partial pressure of CO2 in the adjacent atmosphere would be greater than the content in the aquarium, & an attempt at equilibrium would be constant.
I thought the purpose was to cause skimmable material to rise to the surface of the bubble column and be collected in the cup. Or did you mean that the side effect of the bubbling is diffusion of CO2? I know from my planted tank days that you didn't want to agitate the surface of the water too severely or else you would offgas the CO2. So with that in consideration, most people point power heads / flow at the surface to increase O2 via equilibrium exchange, which would do the same with CO2 (bring to equilibrium) and this is also why tanks in the winter in northern states run lower pH (houses closed up, higher CO2) The CO2 levels of a planted tank are likely desired to be much higher than equilibrium, that's my thinking - keep agitation low and if possible bubble CO2 into the tank to keep it high for the plants. It's difficult to make any kind of FW/SW comparison, even for algae scrubbers. They are 2 totally different animals. So with all this being said about CO2 levels keep in mind the difficultly in comparing SW to FW. Just a few thoughts that's all...rambling...
